Semiconductor device and method of manufacturing the same

ABSTRACT

A semiconductor device with high reliability and operation performance is manufactured without increasing the number of manufacture steps. A gate electrode has a laminate structure. A TFT having a low concentration impurity region that overlaps the gate electrode or a TFT having a low concentration impurity region that does not overlap the gate electrode is chosen for a circuit in accordance with the function of the circuit.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor device having acircuit comprising a thin film transistor (TFT) that uses a crystallinesemiconductor film formed on a substrate (a liquid crystal displaydevice, in particular), and to a method of manufacturing thesemiconductor device. The semiconductor device manufactured inaccordance with the present invention is specifically a liquid crystaldisplay device represented by an active matrix liquid crystal displaydevice in which a pixel portion and a driver circuit to be placed in theperiphery of the pixel portion are formed on the same substrate. Theinvention also relates to electronic appliances that employ the displaydevice as a display unit.

[0003] 2. Description of the Related Art

[0004] TFTs with a crystalline semiconductor film (typically apolysilicon film) on an insulating surface as a semiconductor elementare used for various integrated circuits at present. The TFTs are usedmost often as switching elements of a display device. The TFTs having,as an active layer (a semiconductor layer including a channel formationregion, a source region, and a drain region), a crystallinesemiconductor film, which provides higher mobility than an amorphoussemiconductor film, are high in driving performance, and hence used alsoas elements of a driver circuit. Accordingly, in an active matrix liquidcrystal display device, for example, an image circuit for displaying animage and a driver circuit for controlling the image circuit are formedon a single substrate.

[0005] In an active matrix liquid crystal display device, integratedcircuits such as a pixel circuit for displaying an image, a shiftregister circuit based on a CMOS circuit, a level shifter circuit, abuffer circuit, and a sampling circuit are all arranged on a singlesubstrate while forming different functional blocks. A liquid crystaldisplay device as above has excellent features including being thin,small-sized, light-weight, and low in power consumption. For thatreason, the liquid crystal display device is now used in various scenes;to name a few, as a display unit of a personal computer for space savingand as a display unit of a portable information equipment for obtainingthe latest information anytime, any place.

[0006] A pixel portion of the liquid crystal display device has a TFTfunctioning as a switching element (also called a pixel TFT) and astorage capacitor, and is driven by applying a voltage to a liquidcrystal. The liquid crystal has to be driven with an alternate current,and a method called frame inversion driving is often employed. The TFTis required to have a characteristic of sufficiently low OFF current(Ioff: the value of drain current flowing when the TFT is inoff-operation). However, OFF current is often high when the TFT isformed of a polysilicon film. A known solution for this problem is theLDD structure with a low concentration impurity region (lightly dopeddrain) (a structure in which an impurity region having a lowconcentration is provided between a channel formation region and asource region or a drain region doped with a high concentration ofimpurity element).

[0007] On the other hand, high driving voltage is applied to a buffercircuit and the circuit needs to have a withstand voltage high enough toprevent damage against high voltage. In order to enhance the currentdriving ability, the ON current value has to be sufficiently high (Ion:the value of drain current flowing when the TFT is in on-operation).Degradation of the ON current value due to hot carriers is effectivelyprevented by a known structure called the GOLD (gate-drain overlappedLDD) structure in which a gate electrode partially overlaps an LDDregion (with a gate insulating film interposed therebetween).

[0008] In order to obtain a semiconductor device that meets the requiredperformance, it is necessary to fabricate different TFTs for differentcircuits. However, increased number of masks are needed to form an LDDstructure TFT and a GOLD structure TFT. An increase in number of masksused leads to more manufacture steps, complication of the manufactureprocess, and reduction in yield.

SUMMARY OF THE INVENTION

[0009] The present invention has been made in view of the above, and anobject of the present invention is therefore to provide a semiconductordevice, typically, an active matrix liquid crystal display device, inwhich OFF current of a TFT in a pixel portion is reduced and thereliability of a TFT in a driver circuit is improved (i.e., degradationdue to hot carriers is reduced) without increasing the number of masks.

[0010] A liquid crystal display device is low in light utilizationefficiency, and front light or back light is often used during displayin order to improve visibility. The use of front light or back lightraises power consumption of its display portion, canceling low powerconsumption of the liquid crystal display device itself. Accordingly,another object of the present invention is to provide a display deviceof excellent visibility without increasing the number of manufacturesteps.

[0011] According to the present invention, there is provided asemiconductor device having a TFT that is formed in a pixel portion andan n-channel TFT and a p-channel TFT that constitute a driver circuitprovided in the periphery of the pixel portion, all of the TFTs beingformed on the same substrate, characterized in that the n-channel TFThas a second concentration impurity region that partially overlaps agate electrode, and that the p-channel TFT and the TFT formed in thepixel portion respectively have second concentration impurity regionsthat do not overlap gate electrodes.

[0012] According to the present invention, there is provided asemiconductor device having a TFT that is formed in a pixel portion andan n-channel TFT and a p-channel TFT that constitute a driver circuitprovided in the periphery of the pixel portion, all of the TFTs beingformed on the same substrate, characterized in that the n-channel TFThas a gate electrode composed of a first conductive film and a secondconductive film, the first conductive film contacting the top face of agate insulating film, the second conductive film contacting the top faceof the first conductive film, the first conductive film being longerthan the second conductive film in the channel length direction, thefirst conductive film partially overlapping a second concentrationimpurity region, and characterized in that the p-channel TFT and the TFTformed in the pixel portion respectively have gate electrodes that donot overlap second concentration impurity regions, the gate electrodesbeing composed of the first conductive film that contacts the top faceof the gate insulating film and the second conductive film that contactsthe top face of the first conductive film, the first conductive film andthe second conductive film having the same length in the channel lengthdirection.

[0013] According to the present invention, there is provided asemiconductor device having a driver circuit that is composed of ann-channel TFT, a first p-channel TFT, and a second p-channel TFT,characterized in that: the n-channel TFT has a semiconductor layer, agate insulating film formed on the semiconductor layer, and a gateelectrode formed on the gate insulating film, the semiconductor layerincluding a channel formation region, a source region, a drain region,and a second concentration impurity region: the gate electrode iscomposed of a first conductive film and a second conductive film, thefirst conductive film contacting the top face of the gate insulatingfilm, the second conductive film contacting the top face of the firstconductive film; the second concentration impurity region overlaps thefirst conductive film with the gate insulating film interposedtherebetween; the first p-channel TFT has a semiconductor layer, a gateinsulating film formed on the semiconductor layer, and a gate electrodeformed on the gate insulating film, the semiconductor layer including achannel formation region, a source region, a drain region, and a fifthconcentration impurity region; the channel formation region and the gateelectrode of the first p-channel TFT have substantially the same lengthin the channel length direction: the second p-channel TFT has asemiconductor layer, a gate insulating film formed on the semiconductorlayer, and a gate electrode formed on the gate insulating film, thesemiconductor layer including a channel formation region, a sourceregion, a drain region, and a fifth concentration impurity region; thegate electrode of the second p-channel TFT is composed of a firstconductive film and a second conductive film, the first conductive filmcontacting the top face of the gate insulating film, the secondconductive film contacting the top face of the first conductive film;and the fifth concentration impurity region of the second p-channel TFToverlaps the first conductive film with the gate insulating filminterposed therebetween.

[0014] According to the present invention, there is provided asemiconductor device having a driver circuit that is composed of ann-channel TFT, a first p-channel TFT, and a second p-channel TFT,characterized in that: the n-channel TFT has a semiconductor layer, agate insulating film formed on the semiconductor layer, and a gateelectrode formed on the gate insulating film, the semiconductor layerincluding a channel formation region, a source region, a drain region,and a second concentration impurity region; the gate electrode iscomposed of a first conductive film and a second conductive film, thefirst conductive film contacting the top face of the gate insulatingfilm, the second conductive film contacting the top face of the firstconductive film; the second concentration impurity region overlaps thefirst conductive film with the gate insulating film interposedtherebetween; the first p-channel TFT has a semiconductor layer, a gateinsulating film formed on the semiconductor layer, and a gate electrodeformed on the gate insulating film, the semiconductor layer including achannel formation region, a source region, a drain region, a fifthconcentration impurity region and an offset region: the second p-channelTFT has a semiconductor layer, a gate insulating film formed on thesemiconductor layer, and a gate electrode formed on the gate insulatingfilm, the semiconductor layer including a channel formation region, asource region, a drain region, and a fifth concentration impurityregion; the gate electrode of the second p-channel TFT is composed of afirst conductive film and a second conductive film, the first conductivefilm contacting the top face of the gate insulating film, the secondconductive film contacting the top face of the first conductive film;and the fifth concentration impurity region of the second p-channel TFToverlaps the first conductive film with the gate insulating filminterposed therebetween.

[0015] According to the present invention, there is provided asemiconductor device having a driver circuit and a pixel portion, thedriver circuit being composed of an n-channel TFT, a first p-channelTFT, and a second p-channel TFT, the pixel portion including a TFT and astorage capacitor, characterized in that: the n-channel TFT has asemiconductor layer, a gate insulating film formed on the semiconductorlayer, and a gate electrode formed on the gate insulating film, thesemiconductor layer including a channel formation region, a sourceregion, a drain region, and a second concentration impurity region; thegate electrode is composed of a first conductive film and a secondconductive film, the first conductive film contacting the top face ofthe gate insulating film, the second conductive film contacting the topface of the first conductive film; the second concentration impurityregion overlaps the first conductive film with the gate insulating filminterposed therebetween; the first p-channel TFT has a semiconductorlayer, a gate insulating film formed on the semiconductor layer, and agate electrode formed on the gate insulating film, the semiconductorlayer including a channel formation region, a source region, a drainregion, a fifth concentration impurity region, and an offset region; thesecond p-channel TFT has a semiconductor layer, a gate insulating filmformed on the semiconductor layer, and a gate electrode formed on thegate insulating film, the semiconductor layer including a channelformation region, a source region, a drain region, and a fifthconcentration impurity region: the gate electrode of the secondp-channel TFT is composed of a first conductive film and a secondconductive film, the first conductive film contacting the top face ofthe gate insulating film, the second conductive film contacting the topface of the first conductive film; the fifth concentration impurityregion of the second p-channel TFT overlaps the first conductive filmwith the gate insulating film interposed therebetween: and the TFTformed in the pixel portion has a semiconductor layer that includes achannel formation region, a source region, a drain region, a secondimpurity region, and an offset region.

[0016] Further, according to the present invention, there is provided asemiconductor device having a driver circuit that is composed of ann-channel TFT, a first p-channel TFT, and a second p-channel TFT,characterized in that: the n-channel TFT has a semiconductor layer, agate insulating film formed on the semiconductor layer, and a gateelectrode formed on the gate insulating film, the semiconductor layerincluding a channel formation region, a source region, a drain region,and a second concentration impurity region; the gate electrode iscomposed of a first conductive film and a second conductive film, thefirst conductive film contacting the top face of the gate insulatingfilm, the second conductive film contacting the top face of the firstconductive film; the second concentration impurity region has an L_(ov)region and an L_(off) region, and the L_(ov) region overlaps the firstconductive film with the gate insulating film interposed therebetweenwhereas the L_(off) region does not overlap the first conductive film;and the first p-channel TFT and the second p-channel TFT respectivelyhave semiconductor layers, each of the semiconductor layers including achannel formation region, a source region, a drain region, and a fifthconcentration impurity region.

[0017] In the above present invention, the semiconductor device ischaracterized in that the gate electrodes of the n-channel TFT, thep-channel TFTs, and the TFT formed in the pixel portion are formed of anelement selected from the group consisting of Ta, W, Ti, Mo, Al, and Cu,or formed of an alloy material or a compound material containing anyelement in the group above as its main ingredient.

[0018] In the above present invention, the semiconductor device ischaracterized in that a plurality of protrusions are formed in the pixelportion; the TFT formed in the pixel portion is electrically connectedto a pixel electrode that is uneven: and the uneven portion of the pixelelectrode has a radius of curvature of 0.1 to 0.4 μm, and the unevenportion of the pixel electrode is 0.3 to 3 μm tall.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the accompanying drawings:

[0020]FIGS. 1A to 1C are diagrams showing an embodiment mode of thepresent invention;

[0021]FIGS. 2A to 2C are diagrams showing the embodiment mode of thepresent invention;

[0022]FIGS. 3A to 3C are diagrams showing a process of manufacturing asemiconductor device according to the present invention;

[0023]FIGS. 4A to 4C are diagrams showing a process of manufacturing asemiconductor device according to the present invention;

[0024]FIGS. 5A and 5B are diagrams showing a process of manufacturing asemiconductor device according to the present invention;

[0025]FIG. 6 is a diagram showing the structure of a semiconductordevice according to the present invention;

[0026]FIGS. 7A to 7C are diagrams showing a process of manufacturing asemiconductor device according to the present invention:

[0027]FIGS. 8A to 8C are diagrams showing a process of manufacturing asemiconductor device according to the present invention;

[0028]FIGS. 9A to 9C are diagrams showing a process of manufacturing asemiconductor device according to the present invention;

[0029]FIG. 10 is a diagram showing the top view of a semiconductordevice according to the present invention;

[0030]FIG. 11 is a diagram showing a sectional view of a semiconductordevice according to the present invention;

[0031]FIGS. 12A and 12B are diagrams showing a process of manufacturinga semiconductor device according to the present invention;

[0032]FIGS. 13A and 13B are diagrams showing a process of manufacturinga semiconductor device according to the present invention;

[0033]FIGS. 14A to 14C are diagrams showing a process of manufacturing asemiconductor device according to the present invention;

[0034]FIGS. 15A to 15C are diagrams showing a process of manufacturing asemiconductor device according to the present invention;

[0035]FIGS. 16A to 16C are diagrams showing a process of manufacturing asemiconductor device according to the present invention;

[0036]FIG. 17 is a diagram showing a process of manufacturing asemiconductor device according to the present invention;

[0037]FIGS. 18A to 18C are diagrams showing a process of manufacturing asemiconductor device according to the present invention;

[0038]FIGS. 19A to 19C are diagrams showing a process of manufacturing asemiconductor device according to the present invention;

[0039]FIGS. 20A to 20C are diagrams showing a process of manufacturing asemiconductor device according to the present invention;

[0040]FIGS. 21A to 21C are diagrams showing a process of manufacturing asemiconductor device according to the present invention;

[0041]FIG. 22 is a diagram showing a sectional view of a semiconductordevice according to the present invention;

[0042]FIG. 23 is a circuit block diagram of an active matrix liquidcrystal display device;

[0043]FIG. 24 is a circuit block diagram of an active matrix liquidcrystal display device;

[0044]FIGS. 25A to 25D are diagrams showing an exemplary method ofcrystallizing a semiconductor film;

[0045]FIGS. 26A to 26D are diagrams showing an exemplary method ofcrystallizing a semiconductor film;

[0046]FIGS. 27A and 27B are diagrams showing a process of manufacturinga semiconductor device according to the present invention;

[0047]FIGS. 28A to 28C are diagrams showing a process of manufacturing asemiconductor device according to the present invention;

[0048]FIGS. 29A and 29B are diagrams showing a process of manufacturinga semiconductor device according to the present invention;

[0049]FIG. 30 is a top view of a semiconductor device according to thepresent invention;

[0050]FIGS. 31A and 31B are diagrams showing the circuit structure of anEEMOS circuit and an EDMOS circuit, respectively;

[0051]FIG. 32 is a graph showing results of measuring the reliability ofa TFT manufactured in accordance with the present invention;

[0052]FIG. 33 is a graph showing results of measuring the reliability ofa TFT manufactured in accordance with the present invention;

[0053]FIGS. 34A to 34F are diagrams showing examples of an electronicappliance;

[0054]FIGS. 35A to 35D are diagrams showing examples of an electronicappliance;

[0055]FIGS. 36A to 36C are diagrams showing examples of an electronicappliance;

[0056]FIG. 37 is a graph showing the Id-Vg curve of a TFT manufacturedin accordance with the present invention;

[0057]FIG. 38 is a graph showing the Id-Vg curve of a TFT manufacturedin accordance with the present invention;

[0058]FIG. 39 is a diagram showing a sectional view of an invertercircuit;

[0059]FIG. 40 is a graph showing the Id-Vg curve of a TFT manufacturedin accordance with the present invention;

[0060]FIGS. 41A and 41B are graphs showing the Id-Vg curve of TFTsmanufactured in accordance with the present invention;

[0061]FIG. 42 is a graph showing results of measuring the reliability ofa TFT manufactured in accordance with the present invention;

[0062]FIG. 43 is a graph showing results of measuring the reliability ofa TFT manufactured in accordance with the present invention;

[0063]FIG. 44 is a graph showing results of measuring the reliability ofa TFT manufactured in accordance with the present invention;

[0064]FIGS. 45A and 45B are graphs showing results of measuring thereliability of TFTs manufactured in accordance with the presentinvention;

[0065]FIG. 46 is a diagram showing an embodiment of the presentinvention; and

[0066]FIGS. 47A and 47B are respectively a top view and a sectional viewof an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Embodiment Mode 1

[0067] An embodiment mode of the present invention will be describedwith reference to FIGS. 1A to 2C.

[0068] On a substrate 10, a base insulating film 11 is formed from aninsulating film such as a silicon oxide film, a silicon nitride film,and a silicon oxynitride film. The base insulating film 11 in thisembodiment mode has a two-layer structure 11 a and 11 b. However, thebase insulating film may have a single layer or three or more layers ofthe insulating films given in the above.

[0069] Next, an amorphous semiconductor film is formed on the baseinsulating film 11 to a thickness of 30 to 60 nm. No limitation is puton the material of the amorphous semiconductor film, but the film ispreferably formed of silicon or a silicon germanium (Si_(x)Ge_(1-x);0<x<1, typically x=0.001 to 0.05) alloy. The amorphous semiconductorfilm is then subjected to a known crystallization treatment (such aslaser crystallization, thermal crystallization, or thermalcrystallization using nickel or other catalysts) to form a crystallinesemiconductor film. The obtained crystalline semiconductor film ispatterned into a desired shape to form semiconductor layers 12 to 14.

[0070] After forming the semiconductor layers 12 to 14, the layers maybe doped with an impurity element imparting p-type conductivity in orderto control the threshold of an n-channel TFT. Known impurity elementsthat can give a semiconductor the p type conductivity are elementsbelonging to Group 13 in the periodic table, such as boron (B), aluminum(Al), and gallium (Ga).

[0071] A gate insulating film 15 is formed next to cover the island-likesemiconductor layers 12 to 14. The gate insulating film 15 is formed byplasma CVD or sputtering from an insulating film containing silicon tohave a thickness of 40 to 150 nm. Of course, the gate insulating filmmay be a single layer or a laminate of an insulating film containingsilicon.

[0072] Subsequently formed on the gate insulating film 15 as a laminateare a first conductive film (TaN film) 16 a with a thickness of 20 to100 nm and a second conductive film (W film) 16 b with a thickness of100 to 400 nm. The conductive films may be formed of an element selectedfrom the group consisting of Ta, W, Ti, Mo, Al, and Cu, or formed of analloy material or a compound material containing any element in thegroup above as its main ingredient. Alternatively, a semiconductor film,typically a polycrystalline silicon film, doped with an impurity elementsuch as phosphorus may be used.

[0073] Next, resist masks 17 to 19 are formed by photolithography and afirst etching treatment is conducted by ICP (inductively coupled plasma)etching or other etching methods to form an electrode and a wiring line.The W films 20 b to 22 b are first etched under first etching conditionsto taper the first conductive film around the edge, and then the W films20 b to 22 b and the TaN films 20 a to 22 a are simultaneously etchedunder second etching conditions to form first shape conductive layers 20to 22. Denoted by 26 is a part of the gate insulating film, and regionsthereof that are not covered with the first shape conductive layers 20to 22 are also etched and thinned.

[0074] Then a first doping treatment is conducted, without removing theresist masks, to dope the semiconductor layers with an impurity elementimparting n-type conductivity. Ion doping or ion implantation isemployed for the doping treatment. In the first doping treatment, thefirst shape conductive layers 20 to 22 serve as masks against theimpurity element imparting n-type conductivity to form firstconcentration impurity regions 23 to 25 in a self-aligning manner.

[0075] Still keeping the resist masks in place, a second etchingtreatment is conducted as shown in FIG. 1C. Second shape secondconductive films 27 b to 29 b are formed by anisotropic etching. At thispoint, the first conductive layers and the gate insulating film are alsoetched slightly to form second shape first conductive films 27 a to 29a. As a result, second shape conductive layers 27 to 29 (the firstconductive films 27 a to 29 a and the second conductive films 27 b to 29b) and a gate insulating film 39 are formed.

[0076] A second doping treatment is next conducted without removing theresist masks. In the second doping treatment, the layers are doped withan impurity element imparting n-type conductivity in a dose smaller thanin the first doping treatment and at a high acceleration voltage. Thusformed are second concentration impurity regions 33 to 35 and 36 to 38that are newly formed in the semiconductor layers inside the firstconcentration impurity regions formed in FIG. 1B. In the doping, thesemiconductor layers under the second shape first conductive films 27 ato 29 a are also doped with the impurity element while using the secondshape conductive layers 27 to 29 as masks.

[0077] Thus formed are third concentration impurity regions 36 to 38 andsecond concentration impurity regions 33 to 35. The third concentrationimpurity regions 36 to 38 overlap the second shape first conductivefilms 27 a to 29 a. respectively. The second concentration impurityregions are placed between the first concentration impurity regions andthe third concentration impurity regions (33 is between 30 and 36, 34 isbetween 31 and 37, and 35 is between 32 and 38).

[0078] Then the resist masks are removed. Thereafter, a mask 40 is newlyformed from a resist so as to cover the n-channel TFT of a drivercircuit portion. A third etching treatment is conducted as shown in FIG.2A. The first conductive layers of a p-channel TFT and of the TFT in thepixel portion are etched to form third shape conductive layers 41 and42. At this point, a gate insulating film 43 that is not covered withthe mask 40 is slightly etched and thinned.

[0079] In order to avoid fluctuation caused by the uneven gateinsulating film, the gate insulating film is etched after the resistmask is removed as shown in FIG. 2B. The conductive layers serve asmasks to leave portions of the gate insulating film unetched, therebyforming gate insulating layers 44 to 46.

[0080] Next, resist masks 47 and 48 are newly formed to conduct a thirddoping treatment as shown in FIG. 2B. In the third doping treatment, thesemiconductor layer to be an active layer of the p-channel TFT is dopedwith an impurity element imparting p-type conductivity while using thethird shape conductive layer 41 (41 a and 41 b) as a mask against theimpurity element. As a result, fourth concentration impurity regions 49to 51 are formed in a self-aligning manner.

[0081] In this way, TFTs shown in FIG. 2C are manufactured. An n-channelTFT 71 of a driver circuit 73 includes: the third concentration impurityregion 36 overlapping with the second shape conductive layer 27 forforming a gate electrode (the region 36 is called a GOLD region in thisspecification); the second concentration impurity region 33 formedoutside the gate electrode (the region 33 is called an LDD region inthis specification); and the first concentration impurity regionfunctioning as a source region or a drain region. A reference symbol 72denotes a p-channel TFT of the driver circuit 73. A pixel TFT 74 in thepixel portion has the third concentration impurity region 38 and thesecond concentration impurity region 35 formed outside the gateelectrode (the regions 38 and 35 are both called LDD regions in thisspecification), and has the first concentration impurity region 32functioning as a source region or a drain region.

Embodiment Mode 2

[0082] This embodiment mode describes a method of forming an unevenelectrode with projections formed by the same process that is used toform a TFT in a pixel portion.

[0083] A substrate is prepared by forming an insulating film on asurface of a glass substrate, a quartz substrate, a silicon substrate, ametal substrate, or a stainless steel substrate. A plastic substrate mayalso be used as long as it has a heat resistance against the processtemperature of embodiments. A base insulating film is formed on thesubstrate and a semiconductor layer is formed on the base insulatingfilm.

[0084] The projections can have high reproducibility when formed using aphoto mask. Therefore it is appropriate to form the projections inaccordance with the process of manufacturing a pixel TFT 1203. Anexample of forming the projections by layering the semiconductor layer,a gate insulating film, and a conductive film similar to the manufactureof the pixel TFT 1203 is illustrated in FIGS. 3A to 5B.

[0085] The method of forming the projections is not particularly limitedand a single layer of one of the above films, or a laminate combiningthe above films may be used. For example, the projections may be alaminate of the semiconductor layer and the insulating film, or a singlelayer of the conductive film. In other words, a plurality of projectionscan be formed without increasing the number of steps for manufacturing asemiconductor device.

[0086] The thus formed projections, as well as the pixel TFT formed bythe same process and a TFT in a driver circuit, are covered with aninterlayer insulating film. The curvature of the uneven portion of thepixel electrode can be adjusted by selecting the material of theinsulating film. The radius of curvature of the uneven portion of thepixel electrode is set to 0.1 to 0.4 μm (preferably 0.2 to 2 μm). Whenthe insulating film is an organic resin film, an appropriate organicresin film has a viscosity of 10 to 1000 cp (preferably 40 to 200 cp)(for instance, a polyimide film or an acrylic resin film), so that thesurface of the film shows enough irregularities in accordance with theunderlying uneven region.

[0087] After forming the uneven interlayer insulating film, the pixelelectrode is formed thereon. The surface of the pixel electrode is alsoirregular due to the uneven insulating film. The uneven portion is 0.3to 3 μm tall. With the uneven portion formed on the surface of the pixelelectrode, light can effectively be scattered when incident light isreflected as shown in FIG. 6.

[0088] The projections shown in this embodiment mode are a laminate ofthe semiconductor layer, the gate insulating film, the first conductivefilm, and the second conductive film layered in accordance with theprocess of manufacturing the pixel TFT. However, the projections are notparticularly limited and any layer or film given in the above can form asingle layer or a laminate to serve as the projections. Thus theprojections having a necessary height can be formed without increasingthe number of manufacture steps. One projection is spaced apart from anadjacent projection by 0.1 μm or more, preferably 1 μm.

[0089] The projections desirably vary in size in order to scatter thereflected light better, though no particular limitation is set. Theshape and arrangement of the projections may irregular or regular.Furthermore, the projections do not need to be in any particular placeas long as they are in a region below the pixel electrode whichcorresponds to the display region of the pixel portion.

[0090] An appropriate size of the protrusion when viewed from the aboveis 100 to 400 μm², preferably, 25 to 100 μm².

[0091] In this way, the uneven pixel electrode can be formed withoutincreasing the number of manufacture steps.

Embodiment 1

[0092] Embodiments of the present invention will be described withreference to FIGS. 7A to 11. Here, a detailed description will be givenon a method of forming, simultaneously, on the same substrate, a TFT fora pixel portion and TFTs (an n-channel TFT and a p-channel TFT) for adriver circuit that is provided in the periphery of the pixel portion.

[0093] A substrate 100 may be a glass substrate, a quartz substrate, aceramic substrate, or the like. Alternatively, a silicon substrate, ametal substrate, or a stainless steel substrate may be used if thesurface of the substrate is formed with an insulating film. A plasticsubstrate having a heat resistance against the process temperature ofthis embodiment may also be used.

[0094] As shown in FIG. 7A, a base insulating film 101 is formed on thesubstrate 100 from an insulating film such as a silicon oxide film, asilicon nitride film, and a silicon oxynitride film. The base insulatingfilm 101 in this embodiment has a two-layer structure. However, it maybe a single layer of the insulating films given in the above, or alaminate consisting of more than two layers of the above insulatingfilms. The first layer 101 a of the base insulating film 101 is asilicon oxynitride film 101 a formed to a thickness of 50 to 100 nmusing as reaction gas SiH₄, NH₃, and N₂O. The second layer 101 b of thebase insulating film 101 is a silicon oxynitride film 101 b formed to athickness of 100 to 150 nm using as reaction gas SiH₄, and N₂O. The film101 b is layered on the film 101 a.

[0095] An amorphous semiconductor film is formed next on the baseinsulating film 101. The thickness of the amorphous semiconductor filmis 30 to 60 nm. Though not limited, the material of the amorphoussemiconductor film is preferably silicon or a silicon germanium(Si_(x)Ge_(1-x); 0<x<1, typically x=0.001 to 0.05) alloy. In thisembodiment, the amorphous semiconductor film is formed by plasma CVDusing SiH₄ gas.

[0096] The base insulating film and the amorphous semiconductor film canbe formed by the same film formation method, and therefore the baseinsulating film and the amorphous semiconductor film may be formedsuccessively.

[0097] Next, the amorphous semiconductor film is subjected to a knowncrystallization treatment (such as laser crystallization, thermalcrystallization, or thermal crystallization using nickel or othercatalysts) to form a crystalline semiconductor film. The obtainedcrystalline semiconductor film is patterned into a desired shape. Inthis embodiment, a solution containing nickel is retained to the topface of the amorphous silicon film. The film is then subjected todehydrogenation (at 500° C. for an hour) followed by thermalcrystallization (at 550° C. for four hours) and laser annealingtreatment for improving crystallinity, whereby a crystalline siliconfilm is formed. The crystalline silicon film is patterned byphotolithography to form semiconductor layers 102 to 106.

[0098] After forming the semiconductor layers 102 to 106, the layers maybe doped with an impurity element imparting p-type conductivity in orderto control the threshold (Vth) of an n-channel TFT. Known impurityelements that can give a semiconductor the p type conductivity areelements belonging to Group 13 in the periodic table, such as boron (B),aluminum (Al), and gallium (Ga). In this embodiment, boron (B) is usedin the doping.

[0099] Besides, in the case where the crystalline semiconductor film ismanufactured by the laser crystallization method, a pulse oscillationtype or continuous emission type excimer laser, a YAG laser, or a YVO₄laser may be used. In the case where those lasers are used, it isappropriate to use a method in which laser light radiated from a laseroscillator is condensed by an optical system into a linear beam, and isirradiated to the semiconductor film. The conditions of thecrystallization may be properly selected by an operator.

[0100] A gate insulating film 107 is then formed for covering theisland-like semiconductor layers 102 to 106. The gate insulating film107 is formed of an insulating film containing silicon with a thicknessof from 40 to 150 nm by a plasma CVD method or a sputtering method. Ofcourse, a single layer or a lamination structure of an insulating filmcontaining other silicon can be used for the gate insulating film.

[0101] When the silicon oxide film is used, it can be formed by a plasmaCVD method in which TEOS (tetraethyl orthosilicate) and O₂ are mixed,with a reaction pressure of 40 Pa, a substrate temperature of from 300to 400° C., and discharged at a high frequency (1356 MHz) power densityof 0.5 to 0.8 W/cm². The silicon oxide film thus manufactured can obtaingood characteristics as the gate insulating film by subsequent thermalannealing at 400 to 500° C.

[0102] Then, on the gate insulating film 107, a first conductive film(TaN) 108 and a second conductive film (W) 109 are formed intolamination to have a film thickness of 20 to 100 nm and 100 to 400 nm,respectively. The conductive films forming a gate electrode may beformed of an element selected from the group consisting of Ta, W, Ti,Mo, Al, and Cu, or an alloy material or a compound material containingthe above element as its main constituent. Further, a semiconductor filmtypified by a polycrystalline silicon film doped with an impurityelement such as phosphorus may be used. Besides, any combination may beemployed such as a combination in which the first conductive film isformed of tantalum (Ta) and the second conductive film is formed of W, acombination in which the first conductive film is formed of titaniumnitride (TaN) and the second conductive film is formed of Al, or acombination in which the first conductive film is formed of tantalumnitride (TaN) and the second conductive film is formed of Cu.

[0103] Next, masks 110 to 115 made from resist are formed using aphotolithography method, and a first etching process is performed inorder to form electrodes and wirings. In this embodiment, an ICP(inductively coupled plasma) etching method is used, a gas mixture ofCF₄, Cl₂ and O₂ is used as an etching gas, the gas flow rate is set to25/25/10 sccm, and a plasma is generated by applying a 500 W RF (13.56MHz) power to a coil shape electrode at 1 Pa, thereby performingetching. A 150 W RF (13.56 MHz) power is also applied to the substrateside (sample stage), effectively applying a negative self-bias voltage.The W film is etched with the first etching conditions, and a firstshape conductive film including the taper portion at the end portion isformed.

[0104] Thereafter, the first etching conditions are changed into thesecond etching conditions without removing the masks 110 to 115 made ofresist, a gas mixture of CF₄ and Cl₂ is used as an etching gas, the gasflow rate is set to 30/30 sccm, and a plasma is generated by applying a500 W RF (13.56 MHz) power to a coil shape electrode at 1 Pa, therebyperforming etching for about 30 seconds. A 20 W RF (13.56 MHz) power isalso applied to the substrate side (sample stage), effectively applyinga negative self-bias voltage. The W film and the TaN film are bothetched on the same order with the second etching conditions in which CF₄and Cl₂ are mixed. Note that, the etching time may be increased byapproximately 10 to 20% in order to perform etching without any residueon the gate insulating film.

[0105] In the first etching process, a first shape conductive layer isformed to have a tapered shape at the end portion due to the effect ofthe bias voltage applied to the substrate side by adopting a suitableshape of the masks formed from resist. The angle of the tapered portionsis set to 15 to 45°. Thus, first shape conductive layers 117 to 122(first conductive layers 117 a to 122 a and second conductive layers 117b to 122 b) are formed by the first etching process. Reference numeral116 denotes a gate insulating film, and regions of the gate insulatingfilm, which are not covered by the first shape conductive layers 117 to122, are made thinner by approximately 20 to 50 nm by etching.

[0106] Then, a first doping process is performed to add an impurityelement for imparting n-type conductivity to the semiconductor layerwithout removing the mask made of resist (FIG. 7B). Doping may becarried out by an ion doping method or an ion implantation method. Thecondition of the ion doping method is that a dosage is 1.5×10¹⁵/cm², andan acceleration voltage is 60 to 100 keV. As the impurity element forimparting n-type conductivity, an element belonging to group 15 of theperiodic table, typically phosphorus (P) or arsenic (As) is used. Inthis case, the conductive layers 117 to 121 become masks to the impurityelement imparting n-type conductivity, and the first concentrationimpurity regions 123 to 127 are formed in a self-aligning manner. Theimpurity element imparting n-type conductivity in the concentrationrange of 1×10²⁰ to 1×10²¹ atoms/cm³ is added to the first concentrationimpurity regions 123 to 127.

[0107] Thereafter, as shown in FIG. 7C, the second etching process isperformed without removing the masks made of resist. Here, a gas mixtureof CF₄, Cl₂ and O₂ is used as an etching gas, the gas flow rate is setto 20/20/20 (sccm), and a plasma is generated by applying a 500 W RF(13.56 MHz) power to a coil shape electrode at 1 Pa, thereby performingetching. A 20 W RF (13.56 MHz) power is also applied to the substrateside (sample stage), effectively applying a self-bias voltage which islower than that of the first etching process. According to the thirdetching condition. W film is etched. Thus, according to the thirdetching condition. W film is etched in a different direction to form theconductive films 129 to 134.

[0108] Etching reactions in etching the W film and the TaN film with amixture gas of CF₄ and Cl₂ can be inferred from the kind of radicals orions generated and the vapor pressure of a reaction product. Comparingthe vapor pressure among fluorides and chlorides of W and TaN, the vaporpressure of WF₆, which is a fluoride of W, is extremely high while therest of them, namely, WCl₅, TaF₅, and TaCl₅, have about the same levelof vapor pressure. Therefore the W film and the TaN film are etchedsimilarly with a mixture gas of CF₄ and Cl₂. If the mixture gas is addedwith an appropriate amount of O₂, CF₄ and O₂ reacts to change into COand F and a large amount of F radicals or F ions are generated. As aresult, the W film whose fluoride has high vapor pressure is etched atan increased etching rate. On the other hand, the etching rate of theTaN film does not increase much when F is increased. The surface of theTaN film is slightly oxidized by addition of O₂ to the mixture gasbecause TaN is more easily oxidized than W. The oxide of TaN does notreact with fluorine or chlorine, thereby further lowering the etchingrate of the TaN film. Accordingly, the etching rate of the W film can bedifferentiated from the etching rate of the TaN film so that the W filmis etched faster than the TaN film.

[0109] Next, a second doping treatment is conducted as shown in FIG. 8Awithout removing the resist masks. In the second doping treatment, thelayers are doped with an impurity element imparting n-type conductivityin a dose smaller than in the first doping treatment and at a highacceleration voltage. The acceleration voltage is set to 70 to 120 keV,90 keV, in this embodiment. The dose is set to 1.5×10¹⁴ atoms/cm². Newimpurity regions are thus formed in the semiconductor layers inside thefirst concentration impurity regions formed in FIG. 8B. In the doping,the semiconductor layers under the second shape first conductive layers129 a to 133 a are also doped with the impurity element while using thesecond shape conductive layers 129 to 133 as masks.

[0110] Thus formed are third concentration impurity regions 140 to 144and second concentration impurity regions 135 to 139. The thirdconcentration impurity regions 140 to 144 overlap the second shape firstconductive layers 129 a to 133 a, respectively. The second concentrationimpurity regions are placed between the first concentration impurityregions and the third concentration impurity regions (135 is between 145and 140, 136 is between 146 and 141, 137 is between 147 and 142, 138 isbetween 148 a and 143, and 139 is between 149 and 144).

[0111] Then the resist masks are removed. Thereafter, masks 150 and 151are newly formed from a resist to conduct a third etching treatment asshown in FIG. 8B. SF₆ and Cl₂ are used as the etching gas, the gas flowrate ratio of them is set to 50/10 SCCM, and an RF (13.56 MHz) power of500 W is applied to a coiled electrode at a pressure of 1.3 Pa togenerate plasma for 30 second etching. The substrate side (sample stage)receives an RF (13.56 MHz) power of 10 W to apply a substantiallynegative self-bias voltage. In this way, the TaN film is etched in afuture p-channel TFT and in a future pixel portion TFT under the abovethird etching conditions. Third shape conductive layers 152 to 155 areformed as a result.

[0112] In this specification, a ‘future p-channel TFT’ refers to a TFTin the middle of fabrication which is to serve as a p-channel TFT afterthe fabrication is completed. Similarly, a ‘future n-channel TFT’ refersto an unfinished TFT that is to function as an n-channel TFT after itscompletion.

[0113] The resist masks are removed and the gate insulating film is thenetched as shown in FIG. 8C. CHF₃ is used as the etching gas, the gasflow rate thereof is set to 35 SCCM, and an RF power of 800 W is appliedto generate plasma for the etching. Here, the second shape conductivelayers 129 and 131 and the third shape conductive layers 152 to 155serve as masks to cut off portions of the gate insulating film for eachTFT (157-162).

[0114] Next, as shown in FIG. 9A, the masks 164 to 166 are formed fromresist and a third doping process is performed. In accordance with thethird doping process, forth concentration impurity regions 167 to 172are formed, in which the impurity element imparting conductivityopposite to the above conductivity is added to the semiconductor layerthat becomes an active layer of the p-channel TFT. The third shapeconductive layers 152 and 154 are used as masks to the impurity element,and the impurity element that imparts the p-type conductivity is added,to thereby form the forth concentration impurity regions in aself-aligning manner. In this embodiment, the fourth concentrationimpurity regions 167 to 172 are formed by an ion doping method usingdiborane (B₂H₆). In the third doping process, the semiconductor layerforming the n-channel TFT is covered with the masks 164 and 166 formedfrom resist. Although phosphorus is added to the forth concentrationimpurity regions 167 and 172 at different concentrations in accordancewith the first and second doping processes, the doping process isperformed such that the concentration of the impurity element impartingp-type conductivity is higher in any of the impurity regions. Thus, theimpurity regions function as the source region and the drain region ofthe p-channel TFT so that no problem occurs.

[0115] In accordance with these processes, the impurity regions areformed on the respective semiconductor layers. In this embodiment, allthe impurity regions are formed in a self-aligning manner, with theconductive layer as a mask. The third shape conductive layers 129, 130,152, and 153 which overlap the semiconductor layers function as gateelectrodes. Besides, the conductive layer 155 functions as source wiringand the conductive layer 154 functions as the capacitor wiring which isone of storage capacity.

[0116] Subsequently, the masks 164 and 166 consisting of resist areremoved, and a first interlayer insulating film 173 covering the wholesurface is formed. This first interlayer insulating film 173 is formedof an insulating film containing silicon with a thickness of 100 to 200nm by a plasma CVD method or a sputtering method. In this embodiment, asilicon oxynitride film with a film thickness of 150 nm is formed by aplasma CVD method. Of course, the first interlayer insulating film 173is not particularly limited to the silicon oxynitride film, and otherinsulating films containing silicon may be formed into a single layer ora lamination structure.

[0117] Then, as shown in FIG. 9B, a step of activating the impurityelements added in the respective semiconductor layers is performed. Thisstep is carried out by thermal annealing using an annealing furnace. Thethermal annealing may be performed in a nitrogen atmosphere having anoxygen concentration of 100 ppm or less, preferably 0.1 ppm or less andat 400 to 700° C., typically 500 to 550° C. Note that, in addition tothe thermal annealing method, a laser annealing method, or a rapidthermal annealing method (RTA method) can be applied thereto.

[0118] Note that, in this embodiment, at the same time as the aboveactivation process, nickel used as the catalyst for crystallization isgettered to the regions (145 to 149, 167, 170) containing phosphorus ata high concentration. As a result, mainly nickel concentration of thesemiconductor layer which becomes a channel formation region is lowered.The TFT having a channel formation region thus formed is decreased inoff current value, and has high electric field mobility because of goodcrystallinity, thereby attaining satisfactory characteristics.

[0119] Next, a second interlayer insulating film 174 made of an organicinsulating material is formed on the first interlayer insulating film173. Then, patterning is performed for forming a contact hole reachingthe source wiring 155 and contact holes reaching the respective impurityregions 145, 147, 148 a 167 and 170.

[0120] Then, in a driver circuit 406, wirings 175 to 180 electricallyconnected to the first concentration impurity region and the fourthconcentration impurity region, respectively, are formed. Note that,these wirings are formed by patterning a lamination film of a Ti filmwith a film thickness of 50 to 250 nm and an alloy film (alloy film ofAl and Ti) with a film thickness of 300 to 500 nm.

[0121] Besides, in the pixel portion 1407, a pixel electrode 183, a gatewiring 182, and a connecting electrode 181 are formed (FIG. 9C). Thesource wiring 155 is electrically connected with the pixel TFT 1404 bythe connecting electrode 181. Further, the gate wiring 182 iselectrically connected with a third shape conductive layer 153 (a gateelectrode of the pixel TFT). Furthermore, the pixel electrode 183 iselectrically connected with the drain region of the pixel TFT and withthe semiconductor layer functioning as one of electrodes forming astorage capacity. Preferably as the pixel electrode 183, the filmcomposed of Al or Ag as its main constituent, or a lamination film ofthe films, which is superior in reflection.

[0122] In the manner as described above, the driver circuit 1406including an n-channel TFT 1401, a p-channel TFT 1402, and an n-channelTFT 1403, and the pixel portion 1407 including the pixel TFT 1404 and astorage capacitor 1405 can be formed on the same substrate. In thisspecification, such a substrate is called an active matrix substrate forconvenience.

[0123] The n-channel TFT 1401 of the driver circuit 1406 includes achannel formation region 184, the third concentration impurity region140 (GOLD region) overlapping with the third shape conductive layer 129forming the gate electrode, the second concentration impurity region 135(LDD region) formed outside the gate electrode, and the firstconcentration impurity region 145 functioning as a source region or adrain region. The p-channel TFT 1402 includes a channel formation region185, forth concentration impurity regions 168 and 169, which are formedoutside the gate electrode, and a forth concentration impurity region167 functioning as a source region or a drain region. The n-channel TFT1403 includes a channel formation region 186, the third concentrationimpurity region 142 (GOLD region) overlapping the third shape conductivelayer 131 forming the gate electrode, the second concentration impurityregion 137 (LDD region) formed outside the gate electrode, and the firstconcentration impurity region 147 functioning as a source region or adrain region.

[0124] The pixel TFT 1404 of the pixel portion includes a channelformation region 187, the third concentration impurity region 143 (LDDregion) formed outside the gate electrode, the second concentrationimpurity region 138 (LDD region), and the first concentration impurityregion 148 a functioning as a source region or a drain region. Besides,impurity elements imparting p-type conductivity are added at the sameconcentration as the forth concentration impurity region to therespective semiconductor layers 170 to 172 functioning as one ofelectrodes of the storage capacitor 1405. The storage capacitor 1405 isformed by the capacitor wiring 154 and the semiconductor layers 170 to172 with the insulating film (the same film as the gate insulting film)as a dielectric.

[0125] In this embodiment, an optimal structure is chosen for therespective TFTs constituting the circuits in accordance with circuitspecifications required for the pixel portion and the driver circuit, sothat the operation performance and the reliability of the semiconductordevice are improved. Specifically, the LDD structure or the GOLDstructure is chosen for an n-channel. TFT according to the circuitspecification. Thus a TFT structure giving priority to high-speedoperation or hot carrier countermeasure and a TFT structure givingpriority to low OFF current operation can be formed on the samesubstrate.

[0126] For instance, in the case of an active matrix liquid crystaldisplay device, the n-channel TFTs 1401 and 1403 are suitable for drivercircuits for which high-speed operation is more important, such as ashift register, a frequency dividing circuit, a signal dividing circuit,a level shifter, and a buffer. In other words, a TFT obtains a structurethat places stress on hot carrier countermeasures by having a GOLDregion.

[0127] The pixel TFT 1404 is an n-channel TFT having a structure thatgives priority to low OFF current operation. This TFT is thereforeapplicable to a sampling circuit other than the pixel portion. The TFThas no GOLD region that can increase the OFF current value but has anLDD region and an offset region to obtain low OFF current operation. Inaddition, it has been confirmed that the first concentration impurityregion 148 b is very effective in reducing the OFF current value.

[0128]FIG. 10 shows the top view of a pixel portion on an active matrixsubstrate fabricated in accordance with this embodiment. In FIG. 10,components corresponding to those in FIGS. 7A to 9C are denoted by thesame reference symbols. The sectional view taken along the dot-dashedline A-A′ in FIG. 10 corresponds to the one taken along the dot-dashedline A-A′ in FIG. 9. The sectional view taken along the dot-dashed lineB-B′ in FIG. 10 corresponds to the one taken along the dot-dashed lineB-B′ in FIG. 9.

[0129] As illustrated in the drawings, the active matrix substratehaving the pixel structure of this embodiment is characterized in that,the gate electrode 153 of the pixel TFT and the gate line 182 are formedin different layers so that the semiconductor layer is shielded fromlight by the gate line 182.

[0130] According to the pixel structure of this embodiment, the pixelelectrodes are arranged so that edges of the pixel electrodes overlapthe source wiring line in order to shield gaps between the pixelelectrodes against light without using a black matrix.

[0131] The surfaces of the pixel electrodes according to this embodimentare desirably made uneven by a known method, e.g., the sand blast methodor etching, in order to increase the white light level by preventingregular reflection and scattering the reflected light.

[0132] The pixel structure described above makes it possible to arrangepixel electrodes having a larger area to improve the aperture ratio.

[0133] The manufacture process shown in this embodiment requires onlysix photo masks to fabricate an active matrix substrate (namely, asemiconductor layer pattern mask, a first wiring line pattern mask(including the gate electrode 153 of the pixel TFT, the capacitor wiringline 154, and the source line 155), a pattern mask for formingconductive layers of the p-channel TFT and of the pixel portion TFT, apattern mask for forming the source region and the drain region of thep-channel TFT, a pattern mask for forming contact holes, and a secondwiring pattern mask (including the pixel electrode 183, the connectorelectrode 181, and the gate line 182)). Therefore this embodiment cancontribute to cutting the process and the manufacture cost and improvingthe yield.

[0134]FIG. 11 shows a sectional view of an active matrix substratesuitable for a transmissive liquid crystal display device. Themanufacture process of this substrate is the same as the substrate forthe above reflective liquid crystal display device up through the stepof forming a second interlayer insulating film. On the second interlayerinsulating film, a transparent conductive film is formed and thenpatterned to form a transparent conductive layer 191. The transparentconductive film may be formed of a compound of indium oxide and tinoxide, or a compound of indium oxide and zinc oxide.

[0135] In the driver circuit 1406, wiring lines 175 to 180 electricallyconnected to the first concentration impurity regions or the fourthconcentration impurity regions are formed. The wiring lines are formedby patterning a laminate of a Ti film with a thickness of 50 to 250 nmand an alloy film (of Al and Ti) with a thickness of 300 to 500 nm. Onthe other hand, a pixel electrode 191, a gate line 182, and connectorelectrodes 192 and 193 are formed in the pixel portion 1407. Theconnector electrodes 192 and 193 are formed so as to overlap the pixelelectrode 191. In this way, the active matrix substrate suitable for thetransmissive liquid crystal display can be manufactured when one moremask is used.

[0136] TFTs according to this embodiment have displayed excellentcharacteristics. Of those, the pixel TFT is picked to show its TFTcharacteristic (the V-I characteristic), which is graphed in FIG. 37.The gate leak is also shown in the graph and it is sufficiently low. Thepixel TFT structure of the present invention is particularly capable oflowering OFF current, and also rates well in terms of mobility. OFFcurrent is a drain current flowing when a TFT is in an OFF state.

[0137] While FIG. 37 is a V-I characteristic graph of Samples 1 through8, FIG. 38 shows the TFT characteristic of Sample 3.

[0138] Having the structure of the present invention, Sample 3 shows assmall threshold (Vth) as 0.263 V, which is desirable (Vth is the voltageat the rising point in the V-I characteristic graph). The smaller thedifference becomes, the more the short channel effect is contained.Sample 3 has a mobility of 119.2 cm²/Vs, meaning it is also excellent inmobility (μ_(FE)) that is a parameter indicating easiness for carriersto move. The S value (subthreshold coefficient), which is the reciprocalof the maximum inclination in the rising part of the I-V curve, is 0.196V/decade in Sample 3. When VD=5V, OFF current (I_(OFF2)) is 0.39 pA,whereas ON current (I_(ON2)) is 70 μA. ON current is a drain currentflowing when a TFT is in an ON state. Shift-1 denotes the voltage at therising of the I-V curve.

[0139] As described above, employing the present invention results in asemiconductor device having excellent characteristics.

Embodiment 2

[0140]FIG. 39 shows a p-channel TFT 2100 and an n-channel TFT 2200 of aninverter circuit manufactured in accordance with the present invention.These TFTs are formed on a base insulating film 2002 that is formed on asubstrate 2001.

[0141] The p-channel TFT 2100 has a semiconductor layer 2003, a gateinsulating film 2021, and a gate electrode that is composed of a firstconductive layer 2005 a and a second conductive layer 2005 b. Thesemiconductor layer 2003 includes a channel formation region 2012, asource region 2013 connected with a source electrode 2009, a drainregion 2014 connected with a drain electrode 2018, and an LDD region2015 sandwiched between the drain region and the channel formationregion. Reference symbols 2007 and 2008 denote first and secondinterlayer insulating films, respectively.

[0142] In the gate electrode, the end of the first conductive film 2005a and the end of the second conductive film 2005 b almost coincide witheach other on the source region side whereas the end of the firstconductive film 2005 a on the drain region side is extended outward.This structure is obtained by forming a resist mask in the third etchingtreatment shown in FIG. 8B so as to cover only one side of the gateelectrode.

[0143] Thereafter, the semiconductor layer 2003 in the p-channel TFT isdoped with a p type impurity element by ion doping or the like to forman impurity region in the semiconductor layer. The LDD region 2015 canbe formed by using the first conductive film 2005 a as a mask. In iondoping, it is possible to form the LDD region as well as the sourceregion and the drain region in a single doping treatment by controllingthe acceleration voltage. Instead, the doping treatment may be conductedtwice while optimizing the acceleration voltage, so that formation ofthe LDD region is separated from formation of the source region and thedrain region.

[0144] On the other hand, the n-channel TFT 2200 has a semiconductorlayer 2004, a gate insulating film 2022, and a gate electrode that iscomposed of a first conductive film 2006 a and a second conductive film2006 b. The semiconductor layer 2004 includes a channel formation region2016, a source region 2017 connected with a source electrode 2010, adrain region 2018, and LDD regions 2019 and 2020.

[0145] Similar to the p-channel TFT, the end of the first conductivefilm 2006 a and the end of the second conductive film 2006 b in the gateelectrode of the n-channel TFT 2200 almost coincide with each other onthe source region side whereas the end of the first conductive film 2006a on the drain region side is extended outward. The LDD region 2019 onthe source region side is an LDD region that does not overlap with thegate electrode, whereas the LDD region 2020 on the drain region sideoverlaps the gate electrode.

[0146] The LDD regions overlapping the gate electrodes are formed on thedrain side in the p-channel TFT and the n-channel TFT as describedabove. This eases the electric field intensity near a drain and preventsdegradation of a TFT due to hot carriers. The preventive effect isneeded also in a p-channel TFT especially when the channel length is insubmicron level.

[0147] However, an LDD region overlapping a gate electrode increases aparasitic capacitance applied to the gate electrode and hence is notalways be provided on the source side where there is no need to easeelectric field.

[0148] According to the present invention, it is possible to form theLDD region only on the drain side as shown in FIG. 39. Furthermore, theinvention can readily be applied to the case of employing a minutedesign rule, because the source region, the drain region, and the LDDregion are all formed in a self-aligning manner.

[0149] The TFT structure according to this embodiment can mosteffectively be applied to a TFT in which the position of a drain regionis determined in advance as in an inverter circuit. The TFT structure ofthis embodiment can be combined freely with the manufacture process ofEmbodiment 1 by merely changing the resist mask pattern.

Embodiment 3

[0150] In the p-channel TFT and the n-channel TFT of the invertercircuit shown in Embodiment 2, degradation due to hot carriers is notnoticeable when the driving voltage is 10 V or lower. Then the LDDregion overlapping a gate electrode may not necessarily be formed. Inthis case, the p-channel TFT has the same structure as the p-channel TFT402 shown in FIG. 11 while the n-channel TFT has the same structure asthe n-channel TFT 404 shown in FIG. 11 and takes a single gatestructure.

Embodiment 4

[0151] If the channel length is set to 0.6 μm or less in the activematrix substrate described in Embodiment 1, it is desirable to form theLDD region overlapping a gate electrode also in the p-channel TFT. Inthis case, the LDD region is formed in the same way as the LDD region ofthe n-channel TFT 1401 is formed to obtain the same structure, but isdoped with a p type impurity element. The LDD region is provided only onthe drain side as shown in Embodiment 2, if the direction of a sourceand a drain is already determined as in shift register circuits andbuffer circuits.

Embodiment 5

[0152] This embodiment gives a description of a case of manufacturingTFTs in a different step other than Embodiment 1 with reference to FIGS.12A and 12B. Embodiment 5 is merely different from Embodiment 1 in somesteps and the rest is the same. Therefore the same reference symbols areused in the identical steps. The impurity elements used in doping arealso the same.

[0153] First, the first etching treatment and the first doping treatmentare conducted in accordance with the manufacture process shown inEmbodiment 1 to reach the state illustrated in FIG. 7B.

[0154] Thereafter, etching is made under the second etching conditionswithout removing the resist masks 110 to 115. According to the secondetching conditions, CF₄ and Cl₂ are used as the etching gas, the gasflow rate ratio of them is set to 30/30 SCCM, and an RF (13.56 MHz)power of 500 W is applied to a coiled electrode at a pressure of 1 Pa togenerate plasma for 30 second etching. The substrate side (sample stage)also receives an RF (13.56 MHz) power of 20 W to apply a substantiallynegative self-bias voltage. The conductive film (A), i.e., the TaN film,and the conductive film (B), i.e., the W film are etched to the sameextent under the second etching conditions using a mixture of CF₄ andCl₂. As a result, a first shape gate electrode and wiring lines 217 to223 are formed. The gate electrode is composed of first shape firstconductive films 217 a to 223 a and first shape second conductive films217 b to 223 b.

[0155] A second doping treatment is conducted without removing theresist masks 110 to 115. The semiconductor layers 102 to 106 are dopedwith an impurity element imparting n-type conductivity (hereinafterreferred to as n type impurity element). The doping treatment isachieved by ion doping or ion implantation. The n type impurity elementto be used is an element belonging to Group 15 in the periodic table,typically, phosphorus (P) or arsenic (As). In this treatment, the firstshape gate electrode and capacitance wiring lines 217 to 221 serve asmasks to form first concentration impurity regions 224 a to 224 e in aself-aligning manner (FIG. 12A).

[0156] Still keeping the resist masks 110 to 115 in place, a thirdetching treatment is conducted. CF₄, Cl₂, and O₂ are used as the etchinggas, the gas flow rate ratio of them is set to 20/20/20 SCCM, and an RF(13.56 MHz) power of 500 W is applied to a coiled electrode at apressure of 1.0 Pa to generate plasma for the etching. The substrateside (sample stage) receives an RF (13.56 MHz) power of 20 W for 80second etching treatment. As a result, a second shape gate electrode andwiring lines 225 to 231 are formed. The gate electrode is composed ofsecond shape first conductive films 225 a to 231 a and second shapesecond conductive films 225 b to 231 b.

[0157] Then a third doping treatment is conducted without removing theresist masks 110 to 115. In the third doping treatment, thesemiconductor layers under the second shape first conductive films (TaNfilms) are also doped with an n type impurity element while using thesecond shape conductive layer and capacitance wiring lines 225 to 229 asmasks. Formed as a result of this treatment between the firstconcentration impurity regions and the channel formation regions aresecond concentration impurity regions 232 a to 232 e each containing then type impurity element in a concentration of 1×10¹⁸ to 1×10¹⁹atoms/cm³. The first concentration impurity regions 224 a to 224 e eachcontain the n type impurity element in a concentration of 1×10²⁰ to1×10²¹ atoms/cm³ (FIG. 12B).

[0158] Next, the resist masks 110 to 115 are removed and masks 233 to234 for covering a future n-channel TFT and a future pixel TFT areformed from a resist to conduct a fourth doping treatment. Thesemiconductor layers are doped with a p type impurity element in afuture first p-channel TFT and in a future second p-channel TFT whileusing the second shape conductive layers 226 and 227 and the capacitancewiring line 229 as masks. Fourth concentration impurity regions 235 a to235 c and fifth concentration impurity regions 235 d to 235 f are thusformed in a self-aligning manner. In this embodiment, p type impurityregions are formed by ion doping using diborane (B₂H₆). The fourthconcentration impurity regions (P⁺) 235 a to 235 c each contain the ptype impurity element in a concentration of 2×10²⁰ to 1×10²¹ atoms/cm³.The fifth concentration impurity regions 235 d to 235 f each contain thep type impurity element in a concentration of 2×10¹⁷ to 1×10¹⁹atoms/cm³. Although the semiconductor layers of the p-channel TFTs havepreviously been doped with the n type impurity element, the layers donot have a problem to function as source regions and drain regions ofthe future p-channel TFTs if they are doped with the p type impurityelement in the fourth doping treatment in a concentration higher thanthe concentration of the n type impurity element (FIG. 13A).

[0159] Resist masks 236 and 237 are then used to cover the n-channel TFTand the first p-channel TFT of the driver circuit to conduct a fourthetching treatment. Cl₂ is used as the etching gas, the gas flow ratethereof is set to 80 SCCM, and an RF power of 350 W is applied to acoiled electrode at a pressure of 1.2 Pa to generate plasma for 30second etching. The substrate (sample stage) side receives an RF (13.56MHz) power of 50 W to apply a substantially negative self-bias voltage.Thus formed in the second p-channel TFT of the driver circuit and in thepixel TFT of the pixel portion third shape conductive layers (composedof third shape first conductive films 238 a and 239 a and third shapesecond conductive films 238 b and 239 b) 238 and 239, a capacitancewiring line 240, and wiring lines 241 and 242 (FIG. 13B). Through theabove treatment, the exposed portions of the gate insulating film onwhich the third shape conductive layers are not formed have obtained athickness of about 30 nm in the pixel portion and a thickness of about40 nm in the driver circuit.

[0160] The impurity regions are formed in the respective semiconductorlayers through the above steps. For the subsequent steps to complete theactive matrix substrate, see the step of forming an inorganic interlayerinsulating film and the following steps thereof disclosed in Embodiment1.

[0161] This embodiment can readily be carried out by manufacturing a TFTin accordance with the manufacture process disclosed in Embodiment 1.Although this embodiment describes only the structure of the pixel TFTand the control circuit, other circuits can also be formed on the samesubstrate when following the manufacture process of Embodiment 1.Examples of the other circuits include a signal dividing circuit, afrequency dividing circuit, a D/A converter circuit, an operationamplifier circuit, a γ correction circuit, and a signal processingcircuit (also called a logic circuit) such as a memory circuit and amicroprocessor circuit.

Embodiment 6

[0162] This embodiment gives a description of a case of manufacturingTFTs in a different step other than Embodiment 1 with reference to FIGS.14A to 14C. Embodiment 6 is merely different from Embodiment 1 in somesteps and the rest is the same. Therefore the same reference symbols areused in the identical steps. The impurity elements used in doping arealso the same.

[0163] First, the first etching treatment and the first doping treatmentare conducted in accordance with the manufacture process shown inEmbodiment 1 to reach the state illustrated in FIG. 7B. Thereafter, asecond etching treatment is conducted. CF₄, Cl₂ and O₂ are used as theetching gas, the gas flow rate ratio of them is set to 20/20/20 SCCM,and an RF (13.56 MHz) power of 500 W is applied to a coiled electrode ata pressure of 1.0 Pa to generate plasma for 60 second etching. Thesubstrate (sample stage) side also receives an RF (13.56 MHz) power of20 W to apply a substantially negative self-bias voltage. As a result ofthe second etching treatment, second shape conductive layers 301 to 304and wiring lines 305 to 307 are formed.

[0164] Next, the semiconductor layers are doped with an n type impurityelement through the second shape first conductive films in aself-aligning manner while using the second shape second conductivefilms as masks. Formed as a result of this treatment between the channelformation regions and first concentration impurity regions 308 a to 308e are second concentration impurity regions 308 f to 308 j eachcontaining the n type impurity element in a concentration of 1×10¹⁸ to1×10¹⁹ atoms/cm³. At this point, the first concentration impurityregions 308 a to 308 e each contain the n type impurity element in aconcentration of 1×10²⁰ to 1×10²¹ atoms/cm³.

[0165] Then the resist masks 110 to 115 are removed. Thereafter, masks309 and 310 for covering the n-channel TFT and the pixel TFT are newlyformed from a resist to conduct a third doping treatment. Through thethird doping treatment, the semiconductor layers in the p-channel TFTsare doped with a p type impurity element in a self-aligning manner whileusing the second shape conductive layers as masks. Fourth concentrationimpurity regions 311 a to 311 c and fifth concentration impurity regions311 d to 311 f are thus formed (FIG. 14B).

[0166] The resist masks 309 and 310 are removed, and masks 312 and 313are newly formed from a resist to cover the n-channel TFT and the secondp-channel TFT. Cl₂ is used as the etching gas, the gas flow rate thereofis set to 80 SCCM, and an RF (13.56 MHz) power of 500 W is applied to acoiled electrode at a pressure of 1.2 Pa to generate plasma for 40second etching. The substrate (sample stage) side receives an RF (13.56MHz) power of 10 W to apply a substantially negative self-bias voltage.Thus formed in the first p-channel TFT and in the pixel TFT are thirdshape conductive layers (composed of third shape first conductive films314 a and 315 a and third shape second conductive films 314 b and 315 b)314 and 315, and wiring lines 316 to 318 (FIG. 14C).

[0167] Through the third etching treatment, offset regions 311 g and 311h are formed in the semiconductor layers of the first p-channel TFT andof the pixel TFT, respectively. An offset region in this specificationrefers to a semiconductor layer having the same composition as a channelformation region (meaning, the region contains the same impurity elementas the channel formation region), and the region does not overlap a gateelectrode. The offset regions 311 g and 311 h function as simpleresistors and are very effective in reducing the OFF current value.

[0168] For the subsequent steps to complete the active matrix substrate,see the step of forming an inorganic interlayer insulating film and thefollowing steps thereof disclosed in Embodiment 1.

[0169] This embodiment can readily be carried out by manufacturing a TFTin accordance with the manufacture process disclosed in Embodiment 1.Although this embodiment describes only the structure of the pixel TFTand the control circuit, other circuits can also be formed on the samesubstrate when following the manufacture process of Embodiment 1.Examples of the other circuits include a signal dividing circuit, afrequency dividing circuit, a D/A converter circuit, an operationamplifier circuit, a γ correction circuit, and a signal processingcircuit (also called a logic circuit) such as a memory circuit and amicroprocessor circuit.

Embodiment 7

[0170] This embodiment gives a description of a case of manufacturingTFTs in a different step other than Embodiment 1 with reference to FIGS.15A to 15C. Embodiment 7 is merely different from Embodiment 1 in somesteps and the rest is the same. Therefore the same reference symbols areused in the identical steps.

[0171] First, the first etching treatment and the first doping treatmentare conducted in accordance with the manufacture process shown inEmbodiment 1 to reach the state illustrated in FIG. 7B. Thereafter, asecond etching treatment is conducted. In the second etching treatment,CF₄, Cl₂ and O₂ are used as the etching gas, the gas flow rate ratio ofthem is set to 20/20/20 SCCM, and an RF (13.56 MHz) power of 500 W isapplied to a coiled electrode at a pressure of 1.0 Pa to generate plasmafor 80 second etching. The substrate (sample stage) side receives an RF(13.56 MHz) power of 20 W to apply a substantially negative self-biasvoltage. Thus second shape conductive layers and wiring lines areformed.

[0172] Next, the n-channel TFT and the pixel TFT are covered with resistmasks 401 and 402, respectively, to conduct a second doping treatment.Through the second doping treatment, the semiconductor layers in thep-channel TFTs are doped with a p type impurity element. Thesemiconductor layers are doped with the p type impurity element throughthe second shape first conductive films in a self-aligning manner whileusing the second shape second conductive films as masks. As a result,fourth concentration impurity regions 403 a to 403 c and fifthconcentration impurity regions 403 d to 403 f are formed (FIG. 15A).

[0173] The n-channel TFT and the second p-channel TFT are then coveredwith resist masks 404 and 405, respectively, to conduct a third etchingtreatment. Cl₂ is used as the etching gas, the gas flow rate thereof isset to 80 SCCM, and an RF (13.56 MHz) power of 500 W is applied to acoiled electrode at a pressure of 1.2 Pa to generate plasma for 40second etching. The substrate (sample stage) side receives an RF (13.56MHz) power of 20 W to apply a substantially negative self-bias voltage.Thus third shape conductive layers 406 and 407 and wiring lines 408 to410 are formed (FIG. 15B).

[0174] Next, the resist masks 404 and 405 are removed to conduct a thirddoping treatment. In the third doping treatment, the semiconductorlayers are doped with an n type impurity element to form impurityregions 411 a and 411 b. The semiconductor layers in the p-channel TFTsdo not have a problem to function as source regions and drain regions ofthe p-channel TFTs because the regions have already been doped with thep type impurity element in a concentration higher than the concentrationof the n type impurity element (FIG. 15C).

[0175] After finishing the steps described above, the active matrixsubstrate is completed in accordance with the step of forming aninorganic interlayer insulating film and the following steps thereofdisclosed in Embodiment 1.

[0176] This embodiment can readily be carried out by manufacturing a TFTin accordance with the manufacture process disclosed in Embodiment 1.Although this embodiment describes only the structure of the pixel TFTand the control circuit, other circuits can also be formed on the samesubstrate when following the manufacture process of Embodiment 1.Examples of the other circuits include a signal dividing circuit, afrequency dividing circuit, a D/A converter circuit, an operationamplifier circuit, a γ correction circuit, and a signal processingcircuit (also called a logic circuit) such as a memory circuit and amicroprocessor circuit.

Embodiment 8

[0177] This embodiment gives a description of a case of manufacturingTFTs in a different step other than Embodiment 1 with reference to FIGS.16A to 16C. Embodiment 8 is merely different from Embodiment 1 in somesteps and the rest is the same. Therefore the same reference symbols areused in the identical steps.

[0178] First, the second etching treatment and the second dopingtreatment are conducted in accordance with the manufacture process shownin Embodiment 1 to reach the state illustrated in FIG. 7C.

[0179] Next, a mask 501 is formed from a resist to cover the n-channelTFT and a third etching treatment is conducted. In the third etchingtreatment, Cl₂ is used as the etching gas, the gas flow rate thereof isset to 80 SCCM, and an RF (13.56 MHz) power of 350 W is applied to acoiled electrode at a pressure of 1.2 Pa to generate plasma for 40second etching. The substrate (sample stage) side receives an RF (13.56MHz) power of 50 W to apply a substantially negative self-bias voltage.Thus third shape conductive layers and wiring lines 502 to 507 areformed (FIG. 16B).

[0180] After the resist mask is removed, the gate insulating film isetched. CHF₃ is used as the etching gas, the gas flow rate thereof isset to 35 SCCM, and an RF (13.56 MHz) power of 800 W is applied togenerate plasma for the etching. The substrate (sample stage) sidereceives an RF (13.56 MHz) power of 20 W to apply a substantiallynegative self-bias voltage. Here, the second shape gate electrode servesas a mask for the n-channel TFT whereas the third shape conductivelayers and the capacitance wiring lines serve as masks for the otherTFTs, and portions of the gate insulating film are cut off for each TFTto form gate insulating films 508 to 514 (FIG. 16C).

[0181] Then masks 515 and 516 are newly formed from a resist to conducta third doping treatment. Through the third doping treatment, thesemiconductor layers in the p-channel WF s are doped with a p typeimpurity element while using the third shape gate electrode andcapacitance wiring lines as masks. Fourth concentration impurity regions517 a to 517 c and fifth concentration impurity regions 517 d to 517 fare thus formed in a self-aligning manner (FIG. 17).

[0182] After finishing the steps described above, the active matrixsubstrate is completed in accordance with the step of forming aninorganic interlayer insulating film and the following steps thereofdisclosed in Embodiment 1.

[0183] This embodiment can readily be carried out by manufacturing a TFTin accordance with the manufacture process disclosed in Embodiment 1.Although this embodiment describes only the structure of the pixel TFTand the control circuit, other circuits can also be formed on the samesubstrate when following the manufacture process of Embodiment 1.Examples of the other circuits include a signal dividing circuit, afrequency dividing circuit, a D/A converter circuit, an operationamplifier circuit, a γ correction circuit, and a signal processingcircuit (also called a logic circuit) such as a memory circuit and amicroprocessor circuit.

Embodiment 9

[0184] This embodiment gives a description of a case of manufacturingTFTs in a different step other than Embodiment 1 with reference to FIGS.18A to 18C. Embodiment 9 is merely different from Embodiment 1 in somesteps and the rest is the same. Therefore the same reference symbols areused in the identical steps.

[0185] First, the second etching treatment and the second dopingtreatment are conducted in accordance with the manufacture process shownin Embodiment 1 to reach the state of FIG. 7C where the second shapeconductive layers and wiring lines are formed.

[0186] Next, the n-channel TFT is covered with a resist mask 601 toconduct a third etching treatment. Cl₂ is used as the etching gas, thegas flow rate thereof is set to 80 SCCM, and an RF (13.56 MHz) power of350 W is applied to a coiled electrode at a pressure of 1.2 Pa togenerate plasma for 40 second etching. The substrate (sample stage) sidereceives an RF (13.56 MHz) power of 50 W to apply a substantiallynegative self-bias voltage. Thus third shape conductive layers andwiring lines 602 to 607 are formed (FIG. 18B).

[0187] The resist mask 601 is then removed and masks 608 and 609 arenewly formed from a resist to cover the n-channel TFT and the pixel TFT,respectively. A third doping treatment is conducted and thesemiconductor layers are doped with a p type impurity element to formfourth concentration p type impurity regions 610 a to 610 c and fifthconcentration impurity regions 610 d to 610 f (FIG. 18C).

[0188] After finishing the steps described above, the active matrixsubstrate is completed in accordance with the step of forming aninorganic interlayer insulating film and the following steps thereofdisclosed in Embodiment 1.

[0189] This embodiment can readily be carried out by manufacturing a TFTin accordance with the manufacture process disclosed in Embodiment 1.Although this embodiment describes only the structure of the pixel TFTand the control circuit, other circuits can also be formed on the samesubstrate when following the manufacture process of Embodiment 1.Examples of the other circuits include a signal dividing circuit, afrequency dividing circuit, a D/A converter circuit, an operationamplifier circuit, a γ correction circuit, and a signal processingcircuit (also called a logic circuit) such as a memory circuit and amicroprocessor circuit.

Embodiment 10

[0190] This embodiment gives a description of a case of manufacturingTFTs in a different step other than Embodiment 1 with reference to FIGS.19A to 19C. Embodiment 10 is merely different from Embodiment 1 in somesteps and the rest is the same. Therefore the same reference symbols areused in the identical steps.

[0191] First, the first etching treatment and the first doping treatmentare conducted in accordance with the manufacture process shown inEmbodiment 1 to reach the state illustrated in FIG. 7B. A second etchingtreatment is conducted next. First etching conditions for the secondetching treatment are as follows: CF₄ and Cl₂ are used as the etchinggas, the gas flow rate ratio of them is set to 30/30 SCCM, and an RF(13.56 MHz) power of 500 W is applied to a coiled electrode at apressure of 1.0 Pa to generate plasma for 30 second etching. Thesubstrate (sample stage) side receives an RF (13.56 MHz) power of 20 Wto apply a substantially negative self-bias voltage (FIG. 19B). Thetreatment is then followed by etching under second etching conditions:CF₄, Cl₂ and O₂ are used as the etching gas, the gas flow rate ratio ofthem is set to 20/20/20 SCCM, and an RF (13.56 MHz) power of 500 W isapplied to a coiled electrode at a pressure of 1.0 Pa to generate plasmafor 60 second etching. The substrate (sample stage) side receives an RF(13.56 MHz) power of 20 W to apply a substantially negative self-biasvoltage. Thus second shape conductive layers and wiring lines 701 to 707are formed (FIG. 19C).

[0192] A second doping treatment is conducted next. The semiconductorlayers are doped with an n type impurity element while using the secondshape gate electrode and capacitance wiring lines as masks. As a result,second concentration impurity regions 708 a to 708 e each containing then type impurity element in a concentration of 1×10¹⁸ to 1×10¹⁹ atoms/cm³are formed in a self-aligning manner. At this point, the firstconcentration impurity regions each contain the n type impurity elementin a concentration of 1×10²⁰ to 1×10²¹ atoms/cm³ (FIG. 20A).

[0193] In this embodiment, the second etching treatment is divided intotwo stages to etch the conductive films. The etching treatment under thefirst conditions removes the edges of the first conductive films. Thisresults in formation of L_(ov) regions in which the gate electrodeoverlaps the second concentration impurity regions with the gateinsulating film interposed therebetween and L_(off) regions 719 in whichthe gate electrode does not overlap the second concentration impurityregions.

[0194] Next, a mask 709 is formed from a resist and covers the n-channelTFT to conduct a third etching treatment. In the third etchingtreatment, Cl₂ is used as the etching gas, the gas flow rate thereof isset to 80 SCCM, and an RF (13.56 MHz) power of 350 W is applied to acoiled electrode at a pressure of 1.2 Pa to generate plasma for 40second etching. The substrate (sample stage) side receives an RF (13.56MHz) power of 50 W to apply a substantially negative self-bias voltage.Thus third shape conductive layers and wiring lines 710 to 715 areformed (FIG. 20B).

[0195] Masks 716 and 717 are newly formed from a resist to cover then-channel TFT and the pixel TFT, respectively, in preparation for athird doping treatment. Through the third doping treatment, thesemiconductor layers in the p-channel TFTs are doped with a p typeimpurity element while using the third shape conductive layers and thecapacitance wiring lines as masks. Fourth concentration impurity regions718 a to 718 c and fifth concentration impurity regions 718 d to 718 fare thus formed in a self-aligning manner (FIG. 20C).

[0196] After finishing the steps described above, the active matrixsubstrate is completed in accordance with the step of forming aninorganic interlayer insulating film and the following steps thereofdisclosed in Embodiment 1.

[0197] This embodiment can readily be carried out by manufacturing a TFTin accordance with the manufacture process disclosed in Embodiment 1.Although this embodiment describes only the structure of the pixel TFTand the control circuit, other circuits can also be formed on the samesubstrate when following the manufacture process of Embodiment 1.Examples of the other circuits include a signal dividing circuit, afrequency dividing circuit, a D/A converter circuit, an operationamplifier circuit, a γ correction circuit, and a signal processingcircuit (also called a logic circuit) such as a memory circuit and amicroprocessor circuit.

Embodiment 11

[0198] This embodiment gives a description of a case of manufacturingTFTs in a different step other than Embodiment 1 with reference to FIGS.21A to 21C. Embodiment 11 is merely different from Embodiment 1 in somesteps and the rest is the same. Therefore the same reference symbols areused in the identical steps.

[0199] First, the second etching treatment and the second dopingtreatment are conducted in accordance with the manufacture process shownin Embodiment 1 to reach the state of FIG. 7C where the second shapeconductive layers and the wiring lines are formed.

[0200] Next, resist masks 801 and 802 are formed to cover the futuren-channel TFT and the future second p-channel TFT, respectively, and athird etching treatment is conducted. In the third etching treatment,Cl₂ is used as the etching gas, the gas flow rate thereof is set to 80SCCM, and an RF (13.56 MHz) power of 350 W is applied to a coiledelectrode at a pressure of 1.2 Pa to generate plasma for 40 secondetching. The substrate (sample stage) side receives an RF (13.56 MHz)power of 50 W to apply a substantially negative self-bias voltage. Thusthird shape conductive layers and wiring lines 803 to 807 are formed(FIG. 21B).

[0201] After the resist masks 801 and 802 are removed, masks 808 and 809are newly formed from a resist to cover the n-channel TFT and the pixelTFT, respectively. A third doping treatment is conducted. Through thethird doping treatment, the semiconductor layers in the p-channel TFTsare doped with a p type impurity element while using the third shapeconductive layers and the capacitance wiring lines as masks. Fourthconcentration impurity regions 810 a to 810 c and fifth concentrationimpurity regions 810 d to 810 f are thus formed in a self-aligningmanner (FIG. 21C).

[0202] After finishing the steps described above, the active matrixsubstrate is completed in accordance with the step of forming aninorganic interlayer insulating film and the following steps thereofdisclosed in Embodiment 1.

Embodiment 12

[0203] This embodiment shows results of measuring characteristics ofTFTs manufactured in accordance with manufacture methods disclosed inthis specification.

[0204] First, FIG. 40 shows a graph representing a relation between thedrain current (Id) and the gate voltage (Vg) (hereinafter referred to asId-Vg curve) of a pixel TFT (n-channel TFT) manufactured in accordancewith the manufacture method described in Embodiment 5. The measurementhas been made by setting the source voltage (Vs) to 0 V and the drainvoltage (Vd) to 1 V or 14 V. The measured value of the channel length(L) is 6 μm and the measured value of the channel width (W) is 4 μm.

[0205] OFF current (Ioff) is 0.5 pA when Vd is 14 V.

[0206] Next, FIGS. 41A and 41B respectively show Id-Vg curves of a pixelTFT and a first p-channel TFT of a driver circuit that are obtainedthrough the manufacture method described in Embodiment 8.

[0207] The measurement has been made by setting the source voltage (Vs)to 0 V and the drain voltage (Vd) to 1 V or 14 V. The measured value ofthe channel length (L) is 6 μm and the measured value of the channelwidth (W) is 4 μm in the pixel TFT. The measured value of the channellength (L) is 7 μm and the measured value of the channel width (W) is 8μm in the first p-channel TFT.

[0208] When Vd is 14 V, OFF current (Ioff) of the pixel TFT is 0.3 pAwhereas OFF current (Ioff) of the first p-channel TFT is 2 pA. Comparingthem to a p-channel TFT that has no offset region, the pixel TFT and thefirst p-channel TFT can control sharp rise of Ioff when Vg is high.

[0209] An n-channel TFT, a p-channel TFT, and a pixel TFT manufacturedin accordance with another embodiment of the invention have alsodisplayed excellent characteristics. The n-channel TFT has an Ioff of 10to 30 pA, a field effect mobility of 130 to 180 cm²/Vs, and an S valueof 0.19 to 0.26 V/dec. The p-channel TFT has an Ioff of 2 to 10 pA, afield effect mobility of 70 to 110 cm²/Vs, and an S value of 0.19 to0.25 V/dec. The pixel TFT has an Ioff of 2 to 10 pA, a field effectmobility of 70 to 150 cm²/Vs, and an S value of 0.16 to 0.24 V/dec.

[0210] Now, results of measurement on reliability will be shown.

[0211] The reliability is estimated by checking the ten-year guaranteevoltage. The ten-year guarantee voltage is obtained by inferring astress voltage having a lifetime of ten years from a linear relationprovided by plotting the reciprocal of a stress voltage into asemi-logarithmic graph. The lifetime here is defined as a time a TFTtakes to change its maximum mobility value (μFE_((max))) by 10%. TFTs(driver circuit) manufactured in accordance with the manufacture methodof Embodiment Mode 1 have been measured. The ten-year guarantee voltageof the TFTs is 20 V or higher as shown in FIG. 42, displaying highreliability.

[0212] The thousand-hour life temperature by ON stress is checked next.The temperature at which the characteristic changes by 0.1 V in thousandhours (life temperature) is inferred by plotting the time the TFTcharacteristic (Shift #1) takes to change by 0.1 V when Vg is +20 V (−20V in the p-channel TFT) and Vd is 0V against 1000/T (T: absolutetemperature (K)). As shown in FIG. 43, the thousand-hour lifetemperature is 80° C. or higher in both the n-channel TFT and p-channelTFT.

[0213] The thousand-hour life temperature by OFF stress is checked next.The temperature at which the characteristic changes by 0.1 V in thousandhours (life temperature) is inferred by plotting the time the TFTcharacteristic (Shift #1) takes to change by 0.1 V when Vg is 0V and Vdis +20 V (−20 V in the p-channel TFT) against 1000/T (T: absolutetemperature (K)). As shown in FIG. 44, the thousand-hour lifetemperature is 80° C. or higher in both the n-channel TFT and p-channelTFT.

[0214] The characteristic shift of the n-channel TFT and thecharacteristic shift of the p-channel TFT due to transient stress arechecked next. The ON characteristic shift is observed after twenty hours(at room temperature) when Vd is +20 V (−20 V in the p-channel TFT) andVg is 2 to 6 V (−6 to −2 V in the p-channel TFT). (The transient stressis a stress applied when the drain voltage is set to a certain value andthe gate voltage is set to a certain value.)

[0215]FIGS. 45A and 45B confirm that the change in maximum ratio of thefield effect mobility in twenty hours is limited to 10% or less in boththe n-channel TFT and p-channel TFT.

[0216] These results prove that a manufacture method of the presentinvention can provide highly reliable TFTs having required performancesand can give those excellent TFTs their respective optimal structureswithout increasing the manufacture steps.

Embodiment 13

[0217] The description given in this embodiment with reference to FIG.22 is of a process of manufacturing an active matrix liquid crystaldisplay device from an active matrix substrate that is fabricated inaccordance with the process of one of Embodiments 1 and 5 through 11.

[0218] An active matrix substrate as shown in FIG. 9C is first preparedusing the process of one of Embodiments 1 through 8. An alignment film1181 is formed on the active matrix substrate and subjected to rubbingtreatment. In this embodiment, an organic resin film such as an acrylicresin film is patterned before forming the alignment film 1181 in orderto form in a desired position a columnar spacer 1180 for maintaining adistance between two substrates. Instead of the columnar spacer,spherical spacers may be sprayed onto the entire surface of thesubstrate.

[0219] An opposing substrate 1182 is prepared next. Colored layers 1183and 1184 and a leveling film 1185 are formed on the opposing substrate1182. The red colored layer 1183 partially overlaps the blue coloredlayer 1184 to form a second light shielding portion. Though not shown inFIG. 22, the red colored layer partially overlaps a green colored layerto form a first light shielding portion.

[0220] Then an opposing electrode 1186 is formed in the pixel portion.An alignment film 1187 is formed on the entire surface of the opposingsubstrate 1182 and subjected to rubbing treatment.

[0221] The active matrix substrate on which the pixel portion and thedriver circuit are formed is bonded to the opposing substrate with asealing member. The sealing member has a filler mixed therein. Thefiller, together with the columnar spacer, keeps the distance betweenthe two substrates uniform when the substrates are bonded to each other.Thereafter, a liquid crystal material 1188 is injected between thesubstrates and the device is completely sealed by an end-sealingmaterial (not shown). The liquid crystal material 1188 may be a knownliquid crystal material. Thus an active matrix liquid crystal displaydevice shown in FIG. 22 is completed.

[0222] The number of manufacture steps can be reduced by forming a firstlight shielding portion or a second light shielding portion from coloredlayers to shield gaps between pixels from light as in this embodimentinstead of forming a black mask.

Embodiment 14

[0223]FIG. 23 shows a block diagram of a semiconductor devicemanufactured in accordance with the present invention. This embodimentdescribes a semiconductor device having a source side driver circuit 90,a pixel portion 91, and a gate side driver circuit 92. The term drivercircuit herein collectively refers to a source side driver circuit and agate side driver circuit.

[0224] The source side driver circuit 90 is provided with a shiftregister 90 a, a buffer 90 b, and a sampling circuit (transfer gate) 90c. The gate side driver circuit 92 is provided with a shift register 92a, a level shifter 92 b, and a buffer 92 c. If necessary, a levelshifter circuit may be provided between the sampling circuit and theshift register.

[0225] In this embodiment, the pixel portion 91 is composed of aplurality of pixels, and each of the plural pixels has TFT elements.

[0226] Though not shown in the drawing, another gate side driver circuitmay be provided in across the pixel portion 91 from the gate side drivercircuit 92.

[0227] When the device is digitally driven, the sampling circuit isreplaced by a latch (A) 93 b and a latch (B) 93 c as shown in FIG. 24. Asource side driver circuit 93 is provided with a shift register 93 a,the latch (A) 93 b, the latch (B) 93 c, a D/A converter 93 d, and abuffer 93 e. A gate side driver circuit 95 is provided with a shiftregister 95 a, a level shifter 95 b, and a buffer 95 c. If necessary, alevel shifter circuit may be provided between the latch (B) 93 c and theD/A converter 93 d. A reference symbol 94 denotes a pixel portion.

[0228] The above structure is obtained by employing the manufactureprocess of any of Embodiments 1 through 8. Although this embodimentdescribes only the structure of the pixel portion and the drivercircuit, a memory circuit and a microprocessor circuit can also beformed when following the manufacture process of the present invention.

Embodiment 15

[0229] This embodiment gives a description with reference to FIGS. 25Ato 25D on a process of forming a semiconductor film to serve as anactive layer of a TFT. The crystallization means in this embodiment is atechnique described in Embodiment Mode 1 of Japanese Patent ApplicationLaid-open No. Hei 7-130652.

[0230] First, a base insulating film 1402 with a thickness of 200 nm isformed on a substrate (glass substrate, in this embodiment) 1401 from asilicon oxynitride film. An amorphous semiconductor film (amorphoussilicon film, in this embodiment) 1403 with a thickness of 200 nm isformed thereon. The base insulating film and the amorphous semiconductorfilm may be formed successively without exposing them to the air.

[0231] Next, an aqueous solution containing 10 ppm of catalytic elementby weight (in this embodiment, the catalytic element is nickel and theaqueous solution is nickel acetate aqueous solution) is applied by spincoating to form a catalytic element containing layer 1404 over theentire surface of the amorphous semiconductor film 1403. Examples of thecatalytic element that can be used here other than nickel (Ni) includeiron (Fe), palladium (Pd), tin (Sn), lead (Pb), cobalt (Co), platinum(Pt), copper (Cu), and gold (Au) (FIG. 25A).

[0232] Although spin coating is used in doping of nickel in thisembodiment, a catalytic element may be deposited by evaporation orsputtering to form a thin film (nickel film, in the case of thisembodiment) on the amorphous semiconductor film.

[0233] Prior to the crystallization step, heat treatment is conducted at400 to 500° C. for about an hour to release hydrogen from the film. Thenthe film is subjected to heat treatment at 500 to 650° C. (preferably550 to 570° C.) for four to twelve hours (preferably four to six hours).In this embodiment, the film is heated at 550° C. for four hours to forma crystalline semiconductor film (crystalline silicon film, in thisembodiment) 1405 (FIG. 25B).

[0234] A laser light irradiation step may be inserted here to improvethe crystallinity of the crystalline semiconductor film 1405.

[0235] The next step is gettering for removing nickel used in thecrystallization step from the crystalline silicon film. First, a maskinsulating film 1406 with a thickness of 150 nm is formed on the surfaceof the crystalline semiconductor film 1405 and is patterned to form anopening 1407. Then the exposed portion of the crystalline semiconductorfilm is doped with an element belonging to Group 15 (phosphorus, in thisembodiment). Through this step, a gettering region 1408 containingphosphorus in a concentration of 1×10¹⁹ to 1×10²⁰ atoms/cm³ is formed(FIG. 25C).

[0236] A heat treatment step is carried out next in a nitrogenatmosphere at 450 to 650° C. (preferably 500 to 550° C.) for four totwenty-four hours (preferably six to twelve hours). Through the heattreatment step, nickel in the crystalline semiconductor film moves inthe direction indicated by the arrow and is trapped in the getteringregion 1408 by the gettering action of phosphorus. Since nickel isremoved from the crystalline semiconductor film, the concentration ofnickel contained in the crystalline semiconductor film 1409 is reducedto 1×10¹⁷ atoms/cm³ or lower, preferably 1×10¹⁶ atoms/cm³ (FIG. 25D).

[0237] The crystalline semiconductor film 1409 formed as above has avery high crystallinity owing to the use of a catalytic element forpromoting crystallization (nickel, in this embodiment).

[0238] An alternative method of gettering the catalytic element is toutilize phosphorus (P) as the n type impurity element for doping thesource region or the drain region in the step of activating the impurityelement used to dope the semiconductor film after the inorganicinterlayer insulating film is formed in the manufacture process ofEmbodiment 1.

[0239] The structure of this embodiment can be combined freely with thestructure shown in Embodiment Mode 1 and Embodiments 1 through 8.

Embodiment 16

[0240] This embodiment gives a description with reference to FIGS. 26Ato 26D on a process of forming a semiconductor film to serve as anactive layer of a TFT. Specifically, a technique described in JapanesePatent Application Laid-open No. Hei 10-247735 (corresponding to U.S.Pat. No. 6,165,824) is used.

[0241] First, a base insulating film 1502 with a thickness of 200 nm isformed on a substrate (glass substrate, in this embodiment) 1501 from asilicon oxynitride film. An amorphous semiconductor film (amorphoussilicon film, in this embodiment) 1503 with a thickness of 200 nm isformed thereon. The base insulating film and the amorphous semiconductorfilm may be formed successively without exposing them to the air.

[0242] A mask insulating film 1504 is then formed from a silicon oxidefilm to a thickness of 200 nm. An opening 1505 is formed in the film.

[0243] Next, an aqueous solution containing 100 ppm of catalytic elementby weight (in this embodiment, the catalytic element is nickel and theaqueous solution is nickel acetate aqueous solution) is applied by spincoating to form a catalytic element containing layer 1506. At thispoint, the catalytic element containing layer 1506 selectively contactsthe amorphous semiconductor film 1503 in the region where the opening1505 has been formed. Examples of the catalytic element that can be usedhere other than nickel (Ni) include iron (Fe), palladium (Pd), tin (Sn),lead (Pb), cobalt (Co), platinum (Pt), copper (Cu), and gold (Au) (FIG.26A).

[0244] Although spin coating is used in doping of nickel in thisembodiment, a catalytic element may be deposited by evaporation orsputtering to form a thin film (nickel film, in the case of thisembodiment) on the amorphous semiconductor film.

[0245] Prior to a crystallization step, heat treatment is conducted at400 to 500° C. for about an hour to release hydrogen from the film. Thenthe film is subjected to heat treatment at 500 to 650° C. (preferably550 to 600° C.) for six to sixteen hours (preferably eight to fourteenhours). In this embodiment, the film is heated at 570° C. for fourteenhours. As a result, crystallization starts from the opening 1505 andprogresses in a direction substantially parallel to the substrate (thedirection indicated by the arrow) to form a crystalline semiconductorfilm (crystalline silicon film, in this embodiment) 1507 (FIG. 26B).Macroscopically, the crystal growth direction of the crystallinesemiconductor film 1507 is uniform.

[0246] The next step is gettering for removing nickel used in thecrystallization step from the crystalline silicon film. In thisembodiment, the mask insulating film 1504 previously formed is used as amask without changing anything about the insulating film and thecrystalline semiconductor film is doped with an element belonging toGroup 15 (phosphorus, in this embodiment). A gettering region 1508 isformed as a result in the exposed part of the crystalline semiconductorfilm at the opening 1505. The gettering region 1508 contains phosphorusin a concentration of 1×10¹⁹ to 1×10²⁰ atoms/cm³ is formed (FIG. 26C).

[0247] A heat treatment step is carried out next in a nitrogenatmosphere at 450 to 650° C. (preferably 500 to 550° C.) for four totwenty-four hours (preferably six to twelve hours). Through the heattreatment step, nickel in the crystalline semiconductor film moves inthe direction indicated by the arrow and is trapped in the getteringregion 1508 by the gettering action of phosphorus. Since nickel isremoved from the crystalline semiconductor film, the concentration ofnickel contained in the crystalline semiconductor film 1509 is reducedto 1×10¹⁷ atoms/cm³ or lower, preferably 1×10¹⁶ atoms/cm³ (FIG. 26D).

[0248] The crystalline semiconductor film 1509 formed as above has avery high crystallinity by being crystallized while selectively dopedwith a catalytic element for promoting crystallization (nickel, in thisembodiment). Specifically, the film has a crystal structure in whichrod-like or columnar crystals are arranged in a specific orientation.

[0249] An alternative method of gettering the catalytic element is toutilize phosphorus (P) as the n type impurity element for doping thesource region or the drain region in the step of activating the impurityelement used to dope the semiconductor film after the inorganicinterlayer insulating film is formed in the manufacture process ofEmbodiment 1.

[0250] The structure of this embodiment can be combined freely with thestructure shown in Embodiment Mode 1 and Embodiments 1 through 8.

Embodiment 17

[0251] Described below using FIG. 3A to FIG. 6 (each corresponding toFIG. 27A to FIG. 30) is a method of manufacturing a semiconductor devicein which a TFT for a pixel portion and a TFT for a driver circuitprovided in the periphery of the pixel portion are formed on the samesubstrate. The semiconductor device has a pixel electrode that is unevenbecause of an uneven region formed in the pixel portion by the samemanufacture process as the TFTs.

[0252] A substrate 2100 in this embodiment is made of glass such asbarium borosilicate glass or alumino borosilicate glass, typical exampleof which is Corning #7059 or #1737 glass (a product of CorningIncorporated). The substrate 2100 may be a quartz substrate, a siliconsubstrate, a metal substrate, or a stainless steel substrate if aninsulating film is formed on the surface. A plastic substrate may alsobe used if it has a heat resistance against the process temperature ofthis embodiment.

[0253] On the surface of the substrate 2100, a base insulating film 2101is formed from an insulating film such as a silicon oxide film, asilicon nitride film, and a silicon oxynitride film. In this embodiment,the first layer of the base insulating film 2101 is a silicon oxynitridefilm (composition ratio: Si=32%, O=27%, N=24%, H=17%) 2101 a formed to athickness of 10 to 200 nm (preferably 50 to 100 nm) by plasma CVD usingas reaction gas SiH₄, NH₃, and N₂O. The second layer of the baseinsulating film is a silicon oxynitride film (composition ratio: Si=32%.O=59%, N=7%, H=2%) 2101 b formed to a thickness of 10 to 200 nm(preferably 100 to 150 nm) by plasma CVD using as reaction gas SiH₄ andN₂O. The second layer is layered on the first layer.

[0254] An amorphous semiconductor film is next formed on the baseinsulating film by a known method (such as sputtering, LPCVD, or plasmaCVD). The amorphous semiconductor film is then crystallized by a knowncrystallization treatment (laser crystallization, thermalcrystallization, or thermal crystallization using Ni or other catalyticelement) to form a crystalline semiconductor film. The obtainedcrystalline semiconductor film is patterned into a desired shape to formisland-like semiconductor layers 2102 to 2105 and an island-likesemiconductor layer 2301 for forming projections in the pixel portion(See FIG. 3A). Hereinafter, the projections in this embodiment areformed in accordance with the process of manufacturing a pixel TFT.

[0255] No limitation is put on the material of the crystallinesemiconductor film, but the film is preferably formed of silicon or asilicon germanium (Si_(x)Ge_(1-x); 0<x<1, typically x=0.001 to 0.05)alloy.

[0256] In this embodiment, an amorphous silicon film with a thickness of55 nm is formed by plasma CVD and then irradiated with laser to form acrystalline silicon film. When the semiconductor film is crystallized bylaser treatment, the film is desirably subjected to heat treatment at400 to 500° C. for about an hour in order to reduce the hydrogen contentin the film to 5 atom % or less prior to the crystallization step.

[0257] Another employable crystallization method consists of applying asolution containing Ni to the amorphous silicon film, subjecting thefilm to thermal crystallization treatment (at 550° C., for four hours),and performing laser annealing treatment on the obtained crystallinesilicon film to improve crystallinity of the film. Examples of the laserusable in the laser annealing treatment include pulse oscillation typeor continuous wave KrF excimer laser, XeCl excimer laser, YAG laser, andYVO₄ laser. When one of these lasers is used, laser beams emitted from alaser emitter are collected by an optical system into a linear beam toirradiate the semiconductor film. Conditions for crystallization can beset by an operator suitably.

[0258] Other crystallization methods than the thermal crystallizationinvolving doping of a catalytic element may be employed; thesemiconductor film may be crystallized by heat without using a catalyticelement, or by RTA (rapid thermal annealing) in which the film iscrystallized around 500 to 700° C. After the semiconductor film iscrystallized by RTA, the film may be subjected to laser annealingtreatment to improve its crystallinity.

[0259] The semiconductor layers may be doped with a minute amount ofimpurity element (boron or phosphorus: in this embodiment, boron isused) in order to control threshold of the TFTs.

[0260] Next, a gate insulating film 2106 is formed so as to cover thesemiconductor layers 2102 to 2105 and the island-like semiconductorlayer 2301 for forming the projections. The gate insulating film 2106 isan insulating film containing silicon which is formed by plasma CVD orsputtering to a thickness of 40 to 150 nm. In this embodiment, a siliconoxynitride film (composition ratio: Si=32%, O=59%, N=7%, H=2%) is formedto a thickness of 110 nm by plasma CVD. Needless to say, the gateinsulating film is not limited to a silicon oxynitride film but may be asingle layer or a laminate of other insulating films containing silicon.

[0261] If a silicon oxide film is used, the film is formed by plasma CVDthrough electric discharge while using a mixture of TEOS (tetraethylorthosilicate) and O₂, and setting the reaction pressure to 40 Pa, thesubstrate temperature to 300 to 400° C., and the power density to 0.5 to0.8 W/cm² at a high frequency (13.56 MHz). The silicon oxide film formedin this way can provide excellent characteristics as the gate insulatingfilm when subjected to thermal annealing at 400 to 500° C.

[0262] Formed next on the gate insulating film 2106 are a firstconductive film 2107 with a thickness of 20 to 100 nm and a secondconductive film 2108 with a thickness of 100 to 400 nm. In thisembodiment, the film 2107 is a TaN film having a thickness of 30 nm andthe film 2108 is a W film having a thickness of 370 nm. The TaN film isformed by sputtering in an atmosphere containing nitrogen using a Tatarget. The W film is formed by sputtering using a W target.Alternatively, the W film may be formed by thermal CVD using tungstenhexafluoride (WF₆).

[0263] In either case, the W film has to be less resistive in order touse the film for a gate electrode. The resistivity of the W film isdesirably 20 μΩcm or lower. The W film can have low resistivity when thegrain size is large. However, if the W film contains many impurityelements such as oxygen, crystallization is hindered and the resistivityis raised. Therefore, the W film in this embodiment is formed bysputtering using a highly pure W target (purity: 99.9999%) and takinggreat care not to allow impurities from the air to mix in the film inthe middle of formation. A resistivity of 9 to 20 μΩcm is thus attained.

[0264] Although the first conductive film 2107 is a TaN film whereas thesecond conductive film 2108 is a W film in this embodiment, they are notparticularly limited. Each of the conductive films can be formed of anelement selected from the group consisting of Ta, W, El, Mo, Al, and Cu,or may be formed of an alloy material or compound material containingany of the above elements as its main ingredient. Alternatively, asemiconductor film, typically a polycrystalline silicon film, doped withan impurity element such as phosphorus may be used. The first conductivefilm and the second conductive film can take various combinations, e.g.,a combination of Ta film for the first conductive film 2107 and W filmfor the second conductive film 2108, a combination of TaN film for thefirst conductive film 2107 and Al film for the second conductive film2108, and a combination of TaN film for the first conductive film 2107and Cu film for the second conductive film 2108 (FIG. 27A).

[0265] Next, masks 2109 to 2113 and a mask 2302 for forming theprojections are formed from a resist by photolithography to conduct afirst etching treatment for forming electrodes and wiring lines. Thisembodiment employs ICP (inductively coupled plasma) etching in whichCF₄, Cl₂, and O₂ are used as the etching gas, the gas flow rate ratio ofthem is set to 25/25/10 SCCM, and an RF (13.56 MHz) power of 500 W isapplied to a coiled electrode at a pressure of 1.0 Pa to generate plasmafor the etching. The substrate side (sample stage) receives an RF (13.56MHz) power of 150 W to apply a substantially negative self-bias voltage.

[0266] Thereafter, etching is made under the second etching conditionswithout removing the resist masks 2109 to 2113. According to the secondetching conditions, CF₄ and Cl₂ are used as the etching gas, the gasflow rate ratio of them is set to 30/30 SCCM, and an RF (13.56 MHz)power of 500 W is applied to a coiled electrode at a pressure of 1 Pa togenerate plasma for 30 second etching. The substrate side (sample stage)also receives an RF (13.56 MHz) power of 20 W to apply a substantiallynegative self-bias voltage. The TaN film and the W film are etched tothe same extent under the second etching conditions using a mixture ofCF₄ and Cl₂. Up to this point, first shape conductive layers 2114 to2118 and a conductive film 2303 for forming the projections are formed.

[0267] A first doping treatment is conducted next without removing theresist masks 2109 to 2113. In the first doping treatment, thesemiconductor layers are doped with an impurity element imparting n-typeconductivity (hereinafter referred to as n type impurity element) in aself-aligning manner while using the first shape conductive layers asmasks. The doping treatment is achieved by ion doping or ionimplantation. The n type impurity element to be used is an elementbelonging to Group 15 in the periodic table, typically, phosphorus (P)or arsenic (As). Through the doping, a first concentration impurityregion 2120 having a concentration of 1×10²⁰ to 1×10²¹ atoms/cm³ isformed (FIG. 3B, FIG. 27B).

[0268] Still keeping the resist masks 2109 to 2113 in place, a secondetching treatment is conducted. CF₄, Cl₂, and O₂ are used as the etchinggas, the gas flow rate ratio of them is set to 20/20/20 SCCM, and an RF(13.56 MHz) power of 500 W is applied to a coiled electrode at apressure of 1 Pa to generate plasma for the etching. The substrate side(sample stage) receives an RF (13.56 MHz) power of 20 W to apply aself-bias voltage lower than in the first etching treatment. The W filmis etched under these second etching conditions. As a result, secondshape conductive layers 2121 to 2125 and a conductive film 2304 forforming the projections are formed (FIG. 3C).

[0269] Then a second doping treatment is conducted. Using as a mask thesecond shape first conductive film formed in the first doping treatment,second concentration impurity regions 2126 b to 2129 b are formed on theinside of the n type impurity region 2126 a to 2129 a (on the channelformation region side). The second concentration impurity regions eachcontain an impurity element in a concentration of 1×10¹⁸ to 1×10¹⁹atoms/cm³.

[0270] Next, the resist masks 2109 to 2113 are removed and a mask 2130is newly formed from a resist to conduct a third etching treatment. Cl₂is used as the etching gas, the gas flow rate thereof is set to 80 SCCM,and an RF (13.56 MHz) power of 350 W is applied to a coiled electrode ata pressure of 1.2 Pa to generate plasma for 40 second etching. Thesubstrate side (sample stage) receives an RF (13.56 MHz) power of 50 Wto apply a substantially negative self-bias voltage. Thus the secondshape gate electrodes in the future p-channel TFT of the driver circuitand in the future pixel TFT are etched to form third shape gateelectrodes 2131 and 2132 of the future p-channel TFT and the futurepixel TFT, respectively, and to form a conductive film 2305 for formingthe projections (FIG. 4B, FIG. 28B). In this specification, a ‘futurepixel TFT’ refers to a pixel TFT in the middle of fabrication.Similarly, a ‘future n-channel TFT’ (‘future p-channel TFT’) refers toan unfinished TFT that is to function as an n-channel TFT (p-channelTFT) after its completion.

[0271] A resist mask 2133 is newly formed to cover the future pixel TFTand the uneven region. The future n-channel TFT of the driver circuit iscovered with the mask 2130. Then a third doping treatment is conductedto dope the semiconductor layers in the p-channel TFT and in the storagecapacitor with an impurity element imparting p-type conductivity(hereinafter referred to as p type impurity element). In thisembodiment, the semiconductor layers are doped with a p type impurityelement in a self-aligning manner while using the third shape conductivelayers as masks to form fourth concentration impurity regions. Thisembodiment employs ion doping using diborane (B₂H₆) to form fourthconcentration impurity regions 2134 to 2137.

[0272] The fourth concentration impurity regions are doped with an ntype impurity element (phosphorus (P), in this embodiment) in differentconcentrations. However, all of them do not have a problem to functionas source regions and drain regions of the p-channel TFTs because dopingof impurity elements is performed making sure that those impurityregions contain the p type impurity element in a concentration higherthan the concentration of the n type impurity element.

[0273] Through the above steps, the respective semiconductor layers aredoped with the impurity elements for imparting the respectiveconductivity types and all of the impurity regions are formed in aself-aligning manner while using the gate electrodes as masks.

[0274] The plural projections formed in the pixel portions are obtainedthrough steps identical with the steps of forming the pixel TFT.

[0275] The resist masks 2130, 2133, and 2134 are removed and a firstinterlayer insulating film 2138 is formed to cover the entire surface.In order to make the insulating film susceptive to an uneven region 1207formed in the pixel portion, the first interlayer insulating film 2138is formed from an insulating film containing silicon by plasma CVD orsputtering to a thickness of 200 to 400 nm. In this embodiment, asilicon oxynitride film with a thickness of 400 nm is formed by plasmaCVD. The material of the insulating film is not limited to a siliconoxynitride film and a single layer or a laminate of other insulatingfilms containing silicon may be used.

[0276] The next step is heat treatment for activating the impurityelements used to dope the semiconductor layers. This heat treatment stepfor activation is achieved by heat treatment that uses a furnace(furnace annealing). Conditions of the heat treatment includes preparingnitrogen atmosphere whose oxygen concentration is 1 ppm or less,preferably, 0.1 ppm or less, and setting the temperature to 300 to 500°C., typically 400 to 450° C. In this embodiment, activation is made byheat treatment at 450° C. for four hours. Other than furnace annealing,laser annealing, RTA, or thermal annealing may be adopted.

[0277] If a catalytic element is used in crystallization, theconcentration of Ni used as a catalyst has to be lowered in the channelformation region. Then gettering and the heat treatment activation aresimultaneously conducted, so that nickel is moved to an n type impurityregion that contains a high concentration of phosphorus (P). In thiscase, the temperature of the heat treatment is set to 300 to 700° C.,typically 500 to 550° C. Thus the nickel concentration can be lowered inthe semiconductor layer most part of which is to serve as the channelformation region. If a TFT has a channel formation region formed asabove, the OFF current value thereof is low and crystallinity is high toprovide high field effect mobility, whereby the TFT can have excellentcharacteristics.

[0278] The heat treatment for activation in this embodiment is conductedafter the first interlayer insulating film 2138 is formed. However, thefirst interlayer insulating film 2138 may be formed after the heattreatment. If the material used for the conductive films is weak againstheat, it is preferred to form the interlayer insulating film forprotecting the conductive films before the heat treatment step as inthis embodiment.

[0279] The semiconductor layers are subjected to another heat treatmentin an atmosphere containing 3 to 100% of hydrogen at 300 to 550° C. forone to twelve hours for hydrogenation. In this embodiment, heattreatment is conducted in an atmosphere containing about 3% of hydrogenat 410° C. for an hour. This step is to terminate dangling bonds in thesemiconductor layers by hydrogen contained in the interlayer insulatingfilm. Other hydrogenation measures include plasma hydrogenation(utilizing hydrogen excited by plasma).

[0280] In the case where the activation process is carried out by laserannealing, it is desirable to add laser irradiation by excimer laser,YAG laser, or the like after the hydrogenation described above.

[0281] An alternative is to form a silicon oxynitride film with athickness of 50 to 100 nm as the first interlayer insulating film 2138,conduct heat treatment at 300 to 700° C. (typically 550° C.) for aboutfour hours for activation of the impurity elements used to dope thesemiconductor film, form a silicon nitride film to a thickness of 100 to300 nm, and conduct another heat treatment at 300 to 550° C. for one totwelve hours in a nitrogen atmosphere containing hydrogen.

[0282] Next, a second interlayer insulating film 2139 is formed on thefirst interlayer insulating film 2138. In this embodiment, an acrylicresin film is formed to a thickness of 0.8 to 1.2 μm. Influenced by theuneven region formed in the pixel portion, the second interlayerinsulating film 2139 has uneven surface. The interlayer insulating filmmay be formed without removing the resist mask used to form theprotrusions in order to make the influence of the protrusions clearer.

[0283] Then contact holes reaching the source wiring lines and thesemiconductor layers (impurity regions) of the TFTs are formed throughthe first interlayer insulating film 2138 and the second interlayerinsulating film 2139.

[0284] Wiring lines 2140 to 2145 for electrically connecting the TFTsare formed next. The wiring lines 2140 to 2145 are formed by patterninga laminate of a Ti film with a thickness of 50 to 250 nm and an alloyfilm (an alloy film of Al and Ti) with a thickness of 300 to 500 nm.

[0285] A pixel electrode 2144 is formed in the pixel portion. The pixelelectrode 2144 is desirably formed of a material having excellentreflectivity, such as a film mainly containing Al or Ag, and a laminateof a Al containing film and a Ag containing film. Influenced by theuneven region 1207 formed in a pixel portion 1206, the pixel electrodeis uneven.

[0286] In this embodiment, an end of the pixel electrode 2144 overlaps asource line with the first interlayer insulating film 2138 and thesecond interlayer insulating film 2139 interposed therebetween.Therefore gaps between pixel electrodes can be shielded from lightwithout using a black mask.

[0287] In this way, a driver circuit 1205 that has an n-channel TFT 1201(channel formation region 2146) and a p-channel TFT 1202 (channelformation region 2147) is formed on the same substrate on which thepixel portion 1206 having a pixel TFT 1203 (channel formation region2148), a storage capacitor 1204, and the uneven region 1207 is formed(FIG. 29B). A substrate as such is called an active matrix substrate inthis specification.

[0288]FIG. 30 shows the top view of the active matrix substratemanufactured in accordance with this embodiment. In the case shown inthis embodiment, a source line 2125 and a gate electrode are formed fromthe same conductive film in the same layer (the gate insulating film2119). The pixel portion in this embodiment is provided with the unevenregion 1207.

[0289] The manufacture process shown in this embodiment requires onlysix photo masks to fabricate an active matrix substrate (namely, asemiconductor layer pattern mask, a mask for forming a gate electrode, amask for etching an unnecessary L_(ov) region, a mask for forming forforming a source region and a drain region of a p-channel, a mask forforming contact holes, and a mask for forming a wiring line and a pixelelectrode). Therefore a reflective active matrix substrate in which anuneven region having a plurality of protrusions is formed in a pixelportion to form an uneven pixel electrode can be manufactured withoutcomplicating the manufacture process. This embodiment is thus capable ofcontributing to cutting manufacture cost and improving the yield.

Embodiment 18

[0290] A reflective liquid crystal display device will be described inwhich an electro-optical device manufactured employing the presentinvention is combined with a light source, a reflector, and a lightguide plate.

[0291] An LED or a cold-cathode tube is used for the light source. Thelight source is arranged along a side face of the light guide plate. Thereflector is placed behind the light source. In this specification, thetop face of the light guide plate refers to the face facing a user andthe bottom face of the light guide plate refers to the face opposite tothe top face.

[0292] As shown in FIG. 46, light emitted from the light sourceefficiently enters the interior from the side face of the light guideplate owing to the reflector. The incident light is reflected at a partof the surface which is processed to form a prism and enters and travelsthrough the semiconductor device. The light is then reflected at areflective film provided on the bottom face of the semiconductor device,and goes back through the electro-optical device and the light guideplate to reach eyes of the user.

[0293] The material of the light guide plate may be quarts, inorganicglass (refractive index: 1.42 to 1.7, transmissivity: 80 to 91%) such asborosilicate glass, or a plastic material (resin material). The usableplastic material is a mixture of resins such as a methacrylic resin,typically polymethylmethacrylate known as acryl (refractive index: 1.49,transmissivity: 92 to 93%), polycarbonate (refractive index: 1.59,transmissivity: 88 to 90%), polyarylate (refractive index: 1.61,transmissivity: 85%), poly-4-methylpentene-1 (refractive index: 1.46,transmissivity: 90%), an AS resin [acrylonitrile-styrene polymer](refractive index: 1.57, transmissivity: 90%), and an MS resin[methylmethacrylate-styrene copolymer] (refractive index: 1.56,transmissivity: 90%).

[0294] A semiconductor device manufactured in accordance with any one ofEmbodiments 1 through 11 can be applied to this embodiment.

Embodiment 19

[0295] In the top view of FIG. 47A, an opposing substrate 2151 providedwith a color filter and other components is bonded to an active matrixsubstrate through a sealing member. The active matrix substrate isprovided with a pixel portion, a driver circuit, an external inputterminal 2210 for bonding an FPC (flexible printed circuit), and aconnection wiring line 2211 for connecting the external input terminalto input portions of circuits.

[0296] The FPC is composed of a base film 2213 and a wiring line 2214,and is bonded to the external input terminal by anisotropic conductiveresin 2215. The mechanical strength of the bonding is enhanced by areinforcing plate.

[0297]FIG. 47B shows a sectional view of the external input terminal2210 taken along the line e-e′ in FIG. 47A. Denoted by 2217 is a wiringline formed of a conductive film to form a pixel electrode 2144. Theouter diameter of a conductive particle 2216 is smaller than the pitchof the wiring line 2217. Therefore, when dispersed throughout theadhesive 2215 in an appropriate amount, the conductive particle canestablish an electric connection with the corresponding wiring line onthe FPC side without causing short-circuit with adjacent wiring lines.

[0298] The liquid crystal display panel manufactured as above can beused for a display unit of various electric appliances.

Embodiment 20

[0299] This embodiment describes a case in which pixel TFTs for a pixelportion of a semiconductor device and TFTs for driver circuit of thesemiconductor device all have the same conductivity type (all of themare p-channel TFTs, or all of them are n-channel TFTs). The descriptionis given with reference to FIGS. 31A and 31B.

[0300] A general driver circuit is designed based on a CMOS circuit inwhich an n-channel TFT and a p-channel TFT are combined complementarily.On the other hand, the driver circuit of this embodiment is composedsolely of TFTs having the same conductivity type (p-channel TFT).Accordingly, the mask used in doping an impurity element for controllingthe conductivity type is unnecessary and one less masks can beaccomplished in the manufacturing process of the TFTs. As a result,cutting the manufacture process and manufacture cost is made possible.

[0301] In a PMOS circuit, there are an EEMOS circuit composed ofenhancement type TFTs and an EDMOS circuit composed of a combination ofan enhancement type TFT and a depletion type TFT.

[0302] An example of the EEMOS circuit is shown in FIG. 31A whereas anexample of the EDMOS circuit is shown in FIG. 31B. In FIG. 31A, denotedby 1801 and 1802 are both enhancement type p-channel TFTs (hereinafterreferred to as E type PTFT). In FIG. 31B, 1803 denotes an E type PTFTwhile 1804 denotes a depletion type p-channel TFT (hereinafter referredto as D type PTFT).

[0303] In FIGS. 31A and 31B, VDH denotes a power supply line to which apositive voltage is applied (positive power supply line) and VDL denotesa power supply line to which a negative voltage is applied (negativepower supply line). The negative power supply line may be a power supplyline of a ground electric potential (ground power supply line).

[0304] As described above, the steps of forming an n-channel TFT areeliminated when all the TFTs are p-channel TFTs, thereby simplifying themanufacture process of an active matrix liquid crystal display device.Accompanying the simplification, the yield in the manufacture process isimproved and manufacture cost of the active matrix liquid crystaldisplay device can be reduced.

[0305] The characteristic required for a TFT varies depending on whichcircuit the TFT constitutes. By combining Embodiments 1 through 8, TFTshaving different structures can be formed for different circuits withoutincreasing the number of manufacture steps.

Embodiment 21

[0306] A semiconductor device manufactured in accordance withEmbodiments 1 through 8 employs the GOLD structure that is known to beeffective in preventing degradation of the ON current value due to hotcarriers in order to secure reliability of a TFT of a driver circuit.

[0307] The present inventors have conducted tests on reliability inwhich the optimum value is obtained for the length of a region where agate electrode and a low concentration impurity region overlap in thechannel length direction in the GOLD structure (the length ishereinafter called the length of the L_(ov) region) by setting threekinds of L_(ov) length conditions.

[0308] The characteristic shift of an n-channel TFT due to transientstress is checked. The ON characteristic shift is observed after twentyhours (at room temperature) when Vd is +20 V and Vg is 2 to 6 V. Thetransient stress is a stress applied when the drain voltage is set to acertain value and the gate voltage is set to a certain value. Thepresent inventors use the transient stress to estimate the reliabilityof a TFT.

[0309]FIG. 32 shows results of measuring the transient stress of sampleshaving different L_(ov) lengths. The results in FIG. 32 confirm that thechange in maximum value of the field effect mobility in twenty hours islimited to 10% or less when the L_(ov) length is 1 μm or longer.

[0310] Subsequently, the time the current degradation rate takes toreach 10% is plotted against the reciprocal of the drain voltage. Theten-year guarantee voltage is obtained by inferring a stress voltagehaving a lifetime of ten years from a linear relation provided byplotting the reciprocal of a stress voltage into a semi-logarithmicgraph. The lifetime here is defined as a time a TFT takes to change itsmaximum mobility value (μFE_((max))) by 10%. The present inventors usethe ten-year guarantee voltage to estimate the reliability of a TFT.

[0311]FIG. 33 shows results of obtaining the ten-year guarantee voltagefor varying L_(ov) lengths. The results in FIG. 33 show that a highlyreliable semiconductor device can be obtained when the length of theL_(ov) region is 1 μm or longer, preferably. 1.5 μm or longer.

Embodiment 22

[0312] The CMOS circuit and the pixel portion formed by implementing thepresent invention can be used in an active matrix liquid crystal displaydevice. Namely, the present invention can be implemented for allelectronic equipment that incorporates the semiconductor device (liquidcrystal display device) in its display portion.

[0313] The following can be given as such electronic equipment: a videocamera, a digital camera, a projector (rear type or front type), a headmounted display (goggle type display), a personal computer, and aportable information terminal (such as a mobile computer, a portabletelephone, or an electronic book). Some examples of these are shown inFIGS. 34A to 36C.

[0314]FIG. 34A shows a personal computer, which contains components suchas a main body 5001, an image input portion 5002, a display portion5003, and a keyboard 5004. The present invention can be applied to theimage input portion 5002, the display portion 5003, and other signalcontrol circuits.

[0315]FIG. 34B shows a video camera, which contains components such as amain body 5101, a display portion 5102, an audio input portion 5103,operation switches 5104, a battery 5105, and an image receiving portion5106. The present invention can be applied to the display portion 5102,and other signal control circuits.

[0316]FIG. 34C shows a mobile computer, which contains components suchas a main body 5201, a camera portion 5202, an image receiving portion5203, operation switches 5204, and a display portion 5205. The presentinvention can be applied to the display portion 5205 and other signalcontrol circuits.

[0317]FIG. 34D shows a goggle type display, which contains componentssuch as a main body 5301, a display portion 5302, and arm portions 5303.The present invention can be applied to the display portion 5302 andother signal control circuits.

[0318]FIG. 34E shows a player which uses a recording medium with aprogram recorded therein (hereinafter referred to as a recordingmedium), which contains components such as a main body 5401, a displayportion 5402, a speaker portion 5403, a recording medium 5404, andoperation switches 5405. Note that a DVD (digital versatile disk) or CD(compact disk) is used as the recording medium for this player, and thatappreciation of music or a movie or performing games or the Internet canbe done. The present invention can be applied to the display portion5402 and other signal control circuits.

[0319]FIG. 34F shows a digital camera, which contains components such asa main body 5501, a display portion 5502, an eve piece portion 5503,operation switches 5504, and an image receiving portion (not shown inthe figure). The present invention can be applied to the display portion5502 and other signal control circuits.

[0320]FIG. 35A shows a front type projector, which contains componentssuch as a projecting apparatus 5601 and a screen 5602. The presentinvention can be applied to a liquid crystal display device 5808 whichstructures a portion of the projecting apparatus 5601, and to othersignal control circuits.

[0321]FIG. 35B shows a rear type projector, which contains componentssuch as a main body 5701, a projecting apparatus 5702, a mirror 5703,and a screen 5704. The present invention can be applied to the liquidcrystal display device 5808 which structures a portion of the projectingapparatus 5702, and to other signal control circuits.

[0322] Note that an example of the structure of the projectingapparatuses 5601 and 5702 of FIG. 35A and FIG. 35B is shown in FIG. 35C.The projecting apparatuses 5601 and 5702 are each composed of a lightsource optical system 5801, mirrors 5802 and 5804 to 5806, a dichroicmirror 5803, a prism 5807, the liquid crystal display device 5808, aphase difference plate 5809, and a projecting optical system 5810. Theprojecting optical system 5810 is composed of an optical systemincluding a projection lens. A three-plate type example is shown inEmbodiment 10, but there are no particular limitations, and asingle-plate type may also be used, for example. Further, opticalsystems such as an optical lens, a film having a light polarizingfunction, a film for regulating the phase difference, and an IR film maybe suitably placed in the optical path shown by the arrow in FIG. 35C bythe operator.

[0323] Furthermore. FIG. 35D is a diagram showing one example of thelight source optical system 5801 in FIG. 35C. In Embodiment 22, thelight source optical system 5801 is composed of a reflector 5811, alight source 5812, lens arrays 5813 and 5814, a polarizing conversionelement 5815, and a condenser lens 5816. Note that the light sourceoptical system shown in FIG. 35D is one example, and the light sourceoptical system is not limited to the structure shown in the figure. Forexample, optical systems such as an optical lens, a film having a lightpolarizing function, a film for regulating the phase difference, and anIR film may be suitably added to the light source optical system by theoperator.

[0324] Note that a case using a transmitting type electro-optical devicein the projectors shown in FIG. 35A is shown here, and examples ofapplying a reflecting type electro-optical device and EL display deviceare not shown in the figures.

[0325]FIG. 36A shows a portable telephone, and reference numerals 3001and 3002 denote a display panel and an operation panel, respectively.The display panel 3001 and the operation panel 3002 are connectedthrough a connecting portion 3003. In the connecting portion 3003, anangle θ formed by the surface on which a display portion 3004 of thedisplay panel 3001 is provided and the surface on which operation keys3006 of the operation panel 3002 are provided can be arbitrarilychanged. Further, the portable telephone includes an audio outputportion 3005, the operation keys 3006, a power source switch 3007, andan audio input portion 3008. The present invention can be applied to thedisplay portion 3004.

[0326]FIG. 36B shows a portable book (electronic book), which containscomponents such as a main body 3101, display portions 3102 and 3103, arecording medium 3104, operation switches 3105, and an antenna 3106. Thepresent invention can be applied to the display portions 3102 and 3103,and to other signal control circuits.

[0327]FIG. 36C shows a display, which contains components such as a mainbody 3201, a support stand 3202, and a display portion 3203. The presentinvention can be applied to the display portion 3103. The display of thepresent invention is advantageous for cases of large size screens inparticular, and is advantageous for displays having a diagonal equal toor greater than 10 inches (in particular, equal to or greater than 30inches).

[0328] The applicable range of the present invention is thus extremelywide, and the present invention can be applied to electronic equipmentof all fields. Furthermore, the electronic equipment in this embodimentcan be realized by using a semiconductor device formed in accordancewith any combination of Embodiments 1 to 14.

[0329] By employing the present invention, TFTs whose requiredcharacteristics are different from one another can be formed on the samesubstrate without increasing the number of manufacture steps. Since themanufacture steps do not increase, manufacture cost is lowered and theyield is not reduced. The present invention also can provide a highlyreliable semiconductor device.

[0330] Moreover, the semiconductor device can have excellent visibilityby giving its pixel electrode an uneven surface.

What is claimed is:
 1. A semiconductor device having a TFT that isformed in a pixel portion and an n-channel TFT and a p-channel TFT thatconstitute a driver circuit provided in the periphery of the pixelportion, all of the TFTs being formed on the same substrate, wherein then-channel TFT has a second concentration impurity region that partiallyoverlaps a gate electrode, and wherein the p-channel TFT and the TFTformed in the pixel portion respectively have second concentrationimpurity regions that do not overlap gate electrodes.
 2. A semiconductordevice having a TFT that is formed in a pixel portion and an n-channelTFT and a p-channel TFT that constitute a driver circuit provided in theperiphery of the pixel portion, all of the TFTs being formed on the samesubstrate, wherein the n-channel TFT has a gate electrode comprising afirst conductive film and a second conductive film, the first conductivefilm contacting the top face of a gate insulating film, the secondconductive film contacting the top face of the first conductive film,the first conductive film being longer than the second conductive filmin the channel length direction, the first conductive film partiallyoverlapping a second concentration impurity region, and wherein thep-channel TFT and the TFT formed in the pixel portion respectively havegate electrodes that do not overlap second concentration impurityregions, the gate electrodes comprising the first conductive film thatcontacts the top face of the gate insulating film and the secondconductive film that contacts the top face of the first conductive film,the first conductive film and the second conductive film having the samelength in the channel length direction.
 3. A semiconductor device havinga driver circuit comprising an n-channel TFT, a first p-channel TFT, anda second p-channel TFT, wherein: the n-channel TFT has a semiconductorlayer, a gate insulating film formed on the semiconductor layer, and agate electrode formed on the gate insulating film, the semiconductorlayer including a channel formation region, a source region, a drainregion, and a second concentration impurity region: the gate electrodecomprises a first conductive film and a second conductive film, thefirst conductive film contacting the top face of the gate insulatingfilm, the second conductive film contacting the top face of the firstconductive film; the second concentration impurity region overlaps thefirst conductive film with the gate insulating film interposedtherebetween; the first p-channel TFT has a semiconductor layer, a gateinsulating film formed on the semiconductor layer, and a gate electrodeformed on the gate insulating film, the semiconductor layer including achannel formation region, a source region, a drain region, and a fifthconcentration impurity region; the channel formation region and the gateelectrode of the first p-channel TFT have substantially the same lengthin the channel length direction; the second p-channel TFT has asemiconductor layer, a gate insulating film formed on the semiconductorlayer, and a gate electrode formed on the gate insulating film, thesemiconductor layer including a channel formation region, a sourceregion, a drain region, and a fifth concentration impurity region; thegate electrode of the second p-channel TFT comprises a first conductivefilm and a second conductive film, the first conductive film contactingthe top face of the gate insulating film, the second conductive filmcontacting the top face of the first conductive film; and the fifthconcentration impurity region of the second p-channel TFT overlaps thefirst conductive film with the gate insulating film interposedtherebetween.
 4. A semiconductor device having a driver circuitcomprising an n-channel TFT, a first p-channel TFT, and a secondp-channel TFT, wherein: the n-channel TFT has a semiconductor layer, agate insulating film formed on the semiconductor layer, and a gateelectrode formed on the gate insulating film, the semiconductor layerincluding a channel formation region, a source region, a drain region,and a second concentration impurity region; the gate electrode comprisesa first conductive film and a second conductive film, the firstconductive film contacting the top face of the gate insulating film, thesecond conductive film contacting the top face of the first conductivefilm; the second concentration impurity region overlaps the firstconductive film with the gate insulating film interposed therebetween;the first p-channel TFT has a semiconductor layer, a gate insulatingfilm formed on the semiconductor layer, and a gate electrode formed onthe gate insulating film, the semiconductor layer including a channelformation region, a source region, a drain region, a fifth concentrationimpurity region and an offset region; the second p-channel TFT has asemiconductor layer, a gate insulating film formed on the semiconductorlayer, and a gate electrode formed on the gate insulating film, thesemiconductor layer including a channel formation region, a sourceregion, a drain region, and a fifth concentration impurity region; thegate electrode of the second p-channel TFT comprises a first conductivefilm and a second conductive film, the first conductive film contactingthe top face of the gate insulating film, the second conductive filmcontacting the top face of the first conductive film; and the fifthconcentration impurity region of the second p-channel TFT overlaps thefirst conductive film with the gate insulating film interposedtherebetween.
 5. A semiconductor device having a driver circuit and apixel portion, the driver circuit comprising an n-channel TFT, a firstp-channel TFT, and a second p-channel TFT, the pixel portion including aTFT and a storage capacitor, wherein: the n-channel TFT has asemiconductor layer, a gate insulating film formed on the semiconductorlayer, and a gate electrode formed on the gate insulating film, thesemiconductor layer including a channel formation region, a sourceregion, a drain region, and a second concentration impurity region; thegate electrode comprises a first conductive film and a second conductivefilm, the first conductive film contacting the top face of the gateinsulating film, the second conductive film contacting the top face ofthe first conductive film; the second concentration impurity regionoverlaps the first conductive film with the gate insulating filminterposed therebetween; the first p-channel TFT has a semiconductorlayer, a gate insulating film formed on the semiconductor layer, and agate electrode formed on the gate insulating film, the semiconductorlayer including a channel formation region, a source region, a drainregion, a fifth concentration impurity region, and an offset region; thesecond p-channel TFT has a semiconductor layer, a gate insulating filmformed on the semiconductor layer, and a gate electrode formed on thegate insulating film, the semiconductor layer including a channelformation region, a source region, a drain region, and a fifthconcentration impurity region; the gate electrode of the secondp-channel TFT comprises a first conductive film and a second conductivefilm, the first conductive film contacting the top face of the gateinsulating film, the second conductive film contacting the top face ofthe first conductive film; the fifth concentration impurity region ofthe second p-channel TFT overlaps the first conductive film with thegate insulating film interposed therebetween; and the TFT formed in thepixel portion has a semiconductor layer that includes a channelformation region, a source region, a drain region, a second impurityregion, and an offset region.
 6. A semiconductor device having a drivercircuit comprising an n-channel TFT, a first p-channel TFT, and a secondp-channel TFT, wherein: the n-channel TFT has a semiconductor layer, agate insulating film formed on the semiconductor layer, and a gateelectrode formed on the gate insulating film, the semiconductor layerincluding a channel formation region, a source region, a drain region,and a second concentration impurity region; the gate electrode comprisesa first conductive film and a second conductive film, the firstconductive film contacting the top face of the gate insulating film, thesecond conductive film contacting the top face of the first conductivefilm; the second concentration impurity region has an L_(ov) region andan L_(off) region, wherein the L_(ov) region overlaps the firstconductive film with the gate insulating film interposed therebetween,and wherein the L_(off) region does not overlap the first conductivefilm; and the first p-channel TFT and the second p-channel TFTrespectively have semiconductor layers, each of the semiconductor layersincluding a channel formation region, a source region, a drain region,and a fifth concentration impurity region.
 7. A semiconductor deviceaccording to any one of claims 1 to 6, wherein the gate electrodes ofthe n-channel TFT, the p-channel TFTs, and the TFT formed in the pixelportion comprises an element selected from the group consisting of Ta,W, El, Mo, Al, and Cu, or formed of an alloy material or a compoundmaterial containing any element in the group above as its mainingredient.
 8. A semiconductor device according to any one of claims 1to 6, wherein: a plurality of protrusions are formed in the pixelportion; the TFT formed in the pixel portion is electrically connectedto an uneven pixel electrode; and the uneven portion of the pixelelectrode has a radius of curvature of 0.1 to 0.4 μm, and the unevenportion of the pixel electrode is 0.3 to 3 μm tall.
 9. A semiconductordevice according to any one of claims 1 to 6, wherein: a plurality ofprotrusions are formed in the pixel portion; an interlayer insulatingfilm covering the TFT formed in the pixel portion and the protrusions isformed of an organic resin with a viscosity of 10 to 1000 cp; the TFTformed in the pixel portion is electrically connected to an uneven pixelelectrode; and the uneven portion of the pixel electrode has a radius ofcurvature of 0.1 to 0.4 μm, and the uneven portion of the pixelelectrode is 0.3 to 3 μm tall.
 10. A semiconductor device according toany one of claims 1 to 6, wherein said semiconductor device is a liquidcrystal display device.
 11. A semiconductor device according to any oneof claims 1 to 6, wherein said semiconductor device is one selected fromthe group consisting of a personal computer, a video camera, a mobilecomputer, a goggle type displays a digital camera, a projector, a mobiletelephone, and a portable electronic book.
 12. A method of manufacturinga semiconductor device comprising the steps of: forming a semiconductorlayer on an insulating surface; forming an insulating film on thesemiconductor layer; forming, on the insulating film, a first shapeconductive layer that is a laminate of a first shape first conductivefilm and a first shape second conductive film; forming a firstconcentration impurity region by doping the semiconductor layer with ann type impurity element using the first shape conductive layer as amask; etching the first shape conductive layer electrode to form asecond shape conductive layer that is a laminate of a second shape firstconductive film and a second shape second conductive film; forming asecond concentration impurity region or a third concentration impurityregion by doping the semiconductor layer with an n type impurity elementtransmitted through the second shape first conductive film using thesecond shape second conductive film as a mask; forming a third shapeconductive layer by etching the second shape first conductive film usingthe second shape second conductive film as a mask, the third shapeconductive layer consisting of a laminate of a third shape firstconductive film and a third shape second conductive film: and etching agate insulating film using the third shape conductive layer electrode asa mask.
 13. A method of manufacturing a semiconductor device comprisingthe steps of: forming a semiconductor layer on an insulating surface;forming an insulating film on the semiconductor layer; forming, on theinsulating film, a first shape conductive layer that is a laminate of afirst shape conductive film and a second shape conductive film; forminga first concentration impurity region by doping the semiconductor layerwith an n type impurity element using the first shape conductive layeras a mask; etching the first shape conductive layer to form a secondshape conductive layer that is a laminate of a second shape firstconductive film and a second shape second conductive film; forming asecond concentration impurity region or a third concentration impurityregion by doping the semiconductor layer with an n type impurity elementtransmitted through the second shape first conductive film using thesecond shape second conductive film as a mask; forming a resist mask ina region for forming an n-channel TFT of a driver circuit portion;forming, in a region where the resist mask is not formed, a third shapeconductive layer by etching the second shape first conductive film usingthe second shape second conductive film as a mask, the third shapeconductive layer consisting of a laminate of a third shape firstconductive film and a third shape second conductive film; peeling theresist mask formed; and etching a gate insulating film using the thirdshape conductive layer as a mask.
 14. A method according to claim 12 or13, wherein the second shape conductive layer is shorter than the firstshape conductive layer in the channel length direction.
 15. A methodaccording to claim 12 or 13, wherein the third shape conductive layer isshorter than the first shape conductive layer in the channel lengthdirection, and is shorter than the second shape conductive layer in thechannel length direction.
 16. A method according to claim 12 or 13,wherein said semiconductor device is a liquid crystal display device.17. A method according to claim 12 or 13, wherein said semiconductordevice is one selected from the group consisting of a personal computer,a video camera, a mobile computer, a goggle type display, a digitalcamera, a projector, a mobile telephone, and a portable electronic book.18. A method of manufacturing a semiconductor device comprising thesteps of: forming an amorphous semiconductor film on an insulatingsurface; irradiating the amorphous semiconductor film with laser lightto form a crystalline semiconductor film, thereby completing asemiconductor layer; forming a gate insulating film covering thesemiconductor layer; forming a first conductive film and a secondconductive film on the gate insulating film; etching the firstconductive film and the second conductive film to form a first shapeconductive layer: forming a first concentration impurity region bydoping the semiconductor layer with an n type impurity element; etchingthe first shape conductive layer to form a second shape conductivelayer; doping the semiconductor layer with an n type impurity element toform a second concentration impurity region; forming a fourthconcentration impurity region and a fifth concentration impurity regionby covering an n-channel TFT and a TFT formed in a pixel portion with aresist mask and then doping the semiconductor layer with a p typeimpurity element: and forming a third shape conductive layer by coveringthe n-channel TFT and a second p-channel TFT with a resist mask and thenetching the second shape conductive layer.
 19. A method of manufacturinga semiconductor device comprising the steps of: forming an amorphoussemiconductor film on an insulating surface; irradiating the amorphoussemiconductor film with laser light to form a crystalline semiconductorfilm, thereby completing a semiconductor layer; forming a gateinsulating film covering the semiconductor layer; forming a firstconductive film and a second conductive film on the gate insulatingfilm; etching the first conductive film and the second conductive filmto form a first shape conductive layer; forming a first concentrationimpurity region by doping the semiconductor layer with an n typeimpurity element; etching the first shape conductive layer to form asecond shape conductive layer; doping the semiconductor layer with an ntype impurity element to form a second concentration impurity region;forming a fourth concentration impurity region and a fifth concentrationimpurity region by covering an n-channel TFT and a TFT formed in a pixelportion with a resist mask and then doping the semiconductor layer witha p type impurity element; and forming offset regions respectively inthe semiconductor layer of the TFT formed in the pixel portion and inthe semiconductor layer of a first p-channel TFT by covering then-channel TFT and a second p-channel TFT with a resist mask and thenetching the second shape conductive layer to form a third shapeconductive layer.
 20. A method of manufacturing a semiconductor devicecomprising the steps of: forming an amorphous semiconductor film on aninsulating surface; irradiating the amorphous semiconductor film withlaser light to form a crystalline semiconductor film, thereby completinga semiconductor layer; forming a gate insulating film covering thesemiconductor layer; forming a first conductive film and a secondconductive film on the gate insulating film; etching the firstconductive film and the second conductive film to form a first shapeconductive layer; forming a first concentration impurity region bydoping the semiconductor layer with an n type impurity element; etchingthe first shape conductive layer to form a second shape conductivelayer; forming a fourth concentration impurity region and a fifthconcentration impurity region by covering an n-channel TFT and a TFTformed in a pixel portion with a resist mask and then doping thesemiconductor layer with a p type impurity element; forming a thirdshape conductive layer by covering the n-channel TFT and a secondp-channel TFT with a resist mask and then etching the second shapeconductive layer in a first p-channel TFT and in the TFT formed in thepixel portion; and forming a second concentration impurity region bydoping the semiconductor layer with an n type impurity element.
 21. Amethod of manufacturing a semiconductor device comprising the steps of:forming an amorphous semiconductor film on an insulating surface;irradiating the amorphous semiconductor film with laser light to form acrystalline semiconductor film, thereby completing a semiconductorlayer; forming a gate insulating film covering the semiconductor layer;forming a first conductive film and a second conductive film on the gateinsulating film; etching the first conductive film and the secondconductive film to form a first shape conductive layer; forming a firstconcentration impurity region by doping the semiconductor layer with ann type impurity element; etching the first shape conductive layer toform a second shape conductive layer; doping the semiconductor layerwith an n type impurity element to form a second concentration impurityregion; forming a third shape conductive layer by covering the n-channelTFT with a resist mask and then etching the second shape conductivelayer in a first p-channel TFT, in a second p-channel TFT, and in a TFTformed in a pixel portion; etching the gate insulating film; and forminga fourth concentration impurity region and a fifth concentrationimpurity region by covering the n-channel TFT and the TFT formed in thepixel portion with a resist mask and then doping the semiconductor layerwith a p type impurity element.
 22. A method of manufacturing asemiconductor device comprising the steps of: forming an amorphoussemiconductor film on an insulating surface; irradiating the amorphoussemiconductor film with laser light to form a crystalline semiconductorfilm, thereby completing a semiconductor layer; forming a gateinsulating film covering the semiconductor layer; forming a firstconductive film and a second conductive film on the gate insulatingfilm; etching the first conductive film and the second conductive filmto form a first shape conductive layer; forming a first concentrationimpurity region by doping the semiconductor layer with an n typeimpurity element; etching the first shape conductive layer to form asecond shape conductive layer; doping the semiconductor layer with an ntype impurity element to form a second concentration impurity region;etching the second shape conductive layer after covering an n-channelTFT with a resist mask; and forming a fourth concentration impurityregion and a fifth concentration impurity region by covering then-channel TFT and a TFT formed in a pixel portion with a resist mask andthen doping the semiconductor layer with a p type impurity element. 23.A method of manufacturing a semiconductor device comprising the stepsof: forming an amorphous semiconductor film on an insulating surface;irradiating the amorphous semiconductor film with laser light to form acrystalline semiconductor film, thereby completing a semiconductorlayer; forming a gate insulating film covering the semiconductor layer;forming a first conductive film and a second conductive film on the gateinsulating film; etching the first conductive film and the secondconductive film to form a first shape conductive layer; forming a firstconcentration impurity region by doping the semiconductor layer with ann type impurity element; etching the first shape conductive layer toform a second shape conductive layer; doping the semiconductor layerwith an n type impurity element to form a second concentration impurityregion having a region that overlaps a gate electrode with the gateinsulating film interposed therebetween and a region that does notoverlap the gate electrode; forming a third shape conductive layer bycovering the n-channel TFT with a resist mask and then etching thesecond shape conductive layer in a first p-channel TFT, in a secondp-channel TFT, and in a TFT formed in a pixel portion; and forming afourth concentration impurity region and a fifth concentration impurityregion by covering the n-channel TFT and the TFT formed in the pixelportion with a resist mask and then doping the semiconductor layer witha p type impurity element.
 24. A method of manufacturing a semiconductordevice comprising the steps of: forming an amorphous semiconductor filmon an insulating surface; irradiating the amorphous semiconductor filmwith laser light to form a crystalline semiconductor film, therebycompleting a semiconductor layer; forming a gate insulating filmcovering the semiconductor layer; forming a first conductive film and asecond conductive film on the gate insulating film; etching the firstconductive film and the second conductive film to form a first shapegate electrode and a wiring line; forming a first concentration impurityregion by doping the semiconductor layer with an n type impurityelement; etching the first shape conductive layer to form a second shapeconductive layer; doping the semiconductor layer with an n type impurityelement to form a second concentration impurity region; forming a thirdshape conductive layer by covering an n-channel TFT and a secondp-channel TFT with a resist mask and then etching the second shapeconductive layer; forming a fourth concentration impurity region and afifth concentration impurity region by covering the n-channel TFT and aTFT formed in a pixel portion with a resist mask and then doping thesemiconductor layer with a p type impurity element; and forming aninorganic interlayer insulating film over an entire surface.
 25. Amethod according to any one of claims 18 to 24, wherein the step ofcrystallizing the amorphous semiconductor film includes: introducing theamorphous semiconductor film with an element selected from the groupconsisting of nickel (Ni), iron (Fe), palladium (Pd), tin (Sn), lead(Pb), cobalt (Co), platinum (Pt), copper (Cu), and gold (Au) as acatalytic element for promoting crystallization: heating the amorphoussemiconductor film; and irradiating the crystallized semiconductor filmwith laser light.
 26. A method according to any one of claims 18 to 24,wherein said semiconductor device is a liquid crystal display device.27. A method according to any one of claims 18 to 24, wherein saidsemiconductor device is one selected from the group consisting of apersonal computer, a video camera, a mobile computer, a goggle typedisplay, a digital camera, a projector, a mobile telephone, and aportable electronic book.